Network Layer: Control Plane (Computer Network Course)

Computer Networking: A
Top-Down Approach
8th
edition
Jim Kurose, Keith Ross
Pearson, 2020
Chapter 5
Network Layer:
Control Plane
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Network layer control plane: our goals
understand principles
behind network control
plane:
• traditional routing algorithms
• SDN controllers
• network management,
configuration
 instantiation, implementation
in the Internet:
• OSPF, BGP
• OpenFlow, ODL and ONOS
controllers
• Internet Control Message
Protocol: ICMP
• SNMP, YANG/NETCONF
Network Layer: 5-2

Network layer: “control plane” roadmap
 network management,
configuration
• SNMP
• NETCONF/YANG
introduction
 routing protocols
 link state
 distance vector
 intra-ISP routing: OSPF
 routing among ISPs: BGP
 SDN control plane
 Internet Control Message
Protocol
Network Layer: 5-3

Two approaches to structuring network control plane:
 per-router control (traditional)
 logically centralized control (software defined networking)
Network-layer functions
Network Layer: 5-4
 forwarding: move packets from router’s
input to appropriate router output data plane
control plane
 routing: determine route taken by
packets from source to destination

Per-router control plane
Individual routing algorithm components in each and every
router interact in the control plane
Routing
Algorithm
data
plane
control
plane
1
2
0111
values in arriving
packet header
3
Network Layer: 5-5

Software-Defined Networking (SDN) control plane
Remote controller computes, installs forwarding tables in routers
data
plane
control
plane
Remote Controller
CA
CA CA CA CA
1
2
0111
3
values in arriving
packet header
Network Layer: 5-6

Per-router
control plane
SDN control
plane

configuration
• SNMP
• NETCONF/YANG
 introduction
routing protocols
 link state
 distance vector
Protocol
Network Layer: 5-8

Routing protocol goal: determine “good”
paths (equivalently, routes), from sending
hosts to receiving host, through network of
routers
 path: sequence of routers packets
traverse from given initial source host to
final destination host
 “good”: least “cost”, “fastest”, “least
congested”
 routing: a “top-10” networking challenge!
Routing protocols mobile network
enterprise
network
national or global ISP
datacenter
network
application
transport
network
link
physical
application
transport
network
link
physical
network
link
physical
network
link
physical
network
link
physical
network
link
physical network
link
physical
Network Layer: 5-9

Graph abstraction: link costs
Network Layer: 5-10
u
y
x
w
v
z
2
2
1
3
1
1
2
5
3
5
graph: G = (N,E)
ca,b: cost of direct link connecting a and b
e.g., cw,z = 5, cu,z = ∞
cost defined by network operator:
could always be 1, or inversely related
to bandwidth, or inversely related to
congestion
N: set of routers = { u, v, w, x, y, z }
E: set of links ={ (u,v), (u,x), (v,x), (v,w), (x,w), (x,y), (w,y), (w,z), (y,z) }

Routing algorithm classification
Network Layer: 5-11
global or decentralized information?
global: all routers have complete
topology, link cost info
• “link state” algorithms
decentralized: iterative process of
computation, exchange of info with neighbors
• routers initially only know link costs to
attached neighbors
• “distance vector” algorithms
How fast
do routes
change?
dynamic: routes change
more quickly
• periodic updates or in
response to link cost
changes
static: routes change
slowly over time

configuration
• SNMP
• NETCONF/YANG
 introduction
 link state
 distance vector
Protocol
Network Layer: 5-12

Dijkstra’s link-state routing algorithm
Network Layer: 5-13
 centralized: network topology, link
costs known to all nodes
• accomplished via “link state
broadcast”
• all nodes have same info
 computes least cost paths from one
node (“source”) to all other nodes
• gives forwarding table for that node
 iterative: after k iterations, know
least cost path to k destinations
 cx,y: direct link cost from node
x to y; = ∞ if not direct
neighbors
 D(v): current estimate of cost
of least-cost-path from source
to destination v
 p(v): predecessor node along
path from source to v
 N': set of nodes whose least-
cost-path definitively known
notation

Dijkstra’s link-state routing algorithm
Network Layer: 5-14
1 Initialization:
2 N' = {u} /* compute least cost path from u to all other nodes */
3 for all nodes v
4 if v adjacent to u /* u initially knows direct-path-cost only to direct neighbors */
5 then D(v) = cu,v /* but may not be minimum cost! */
6 else D(v) = ∞
7
8 Loop
9
10
11
12
13
14
15 until all nodes in N'
find w not in N' such that D(w) is a minimum
add w to N'
update D(v) for all v adjacent to w and not in N' :
D(v) = min ( D(v), D(w) + cw,v )
/* new least-path-cost to v is either old least-cost-path to v or known
least-cost-path to w plus direct-cost from w to v */

Dijkstra’s algorithm: an example
Step
0
1
2
3
4
5
N' D(v),p(v) D(x),p(x) D(y),p(y) D(z),p(z)
u
y
x
w
v
z
2
2
1
3
1
1
2
5
3
5
D(w),p(w)
5,u ∞
∞
1,u
2,u
u
v w x y z
Initialization (step 0):
For all a: if a adjacent to u then D(a) = cu,a

Step
0
1
2
3
4
5
D(w),p(w)
5,u ∞
∞
1,u
2,u
u
8 Loop
9
10
find a not in N' such that D(a) is a minimum
add a to N'
ux
v w x y z
u
y
x
w
v
z
2
2
1
3
1
1
2
5
3
5

Step
0
1
2
3
4
5
D(w),p(w)
5,u ∞
∞
1,u
2,u
u
8 Loop
9
10
11
add a to N'
ux
v w x y z
u
y
x
w
v
z
2
2
1
3
1
1
2
5
3
5
update D(b) for all b adjacent to a and not in N' :
D(b) = min ( D(b), D(a) + ca,b )
∞
2,x
4,x
2,u
D(v) = min ( D(v), D(x) + cx,v ) = min(2, 1+2) = 2
D(w) = min ( D(w), D(x) + cx,w ) = min (5, 1+3) = 4
D(y) = min ( D(y), D(x) + cx,y ) = min(inf,1+1) = 2

Step
0
1
2
3
4
5
D(w),p(w)
5,u ∞
∞
1,u
2,u
u
8 Loop
9
10
add a to N'
ux
v w x y z
u
y
x
w
v
z
2
2
1
3
1
1
2
5
3
5
∞
2,x
4,x
2,u
uxy

Step
0
1
2
3
4
5
D(w),p(w)
5,u ∞
∞
1,u
2,u
u
8 Loop
9
10
11
add a to N'
ux
v w x y z
u
y
x
w
v
z
2
2
1
3
1
1
2
5
3
5
∞
2,x
4,x
2,u
uxy
D(b) = min ( D(b), D(a) + ca,b )
4,y
3,y
2,u
D(w) = min ( D(w), D(y) + cy,w ) = min (4, 2+1) = 3
D(z) = min ( D(z), D(y) + cy,z ) = min(inf,2+2) = 4

Step
0
1
2
3
4
5
D(w),p(w)
5,u ∞
∞
1,u
2,u
u
8 Loop
9
10
add a to N'
ux
v w x y z
u
y
x
w
v
z
2
2
1
3
1
1
2
5
3
5
∞
2,x
4,x
2,u
uxy 4,y
3,y
2,u
uxyv

D(b) = min ( D(b), D(a) + ca,b )
D(w) = min ( D(w), D(v) + cv,w ) = min (3, 2+3) = 3
Step
0
1
2
3
4
5
D(w),p(w)
5,u ∞
∞
1,u
2,u
u
8 Loop
9
10
11
add a to N'
ux
v w x y z
u
y
x
w
v
z
2
2
1
3
1
1
2
5
3
5
∞
2,x
4,x
2,u
uxy 4,y
3,y
2,u
uxyv 4,y
3,y

Step
0
1
2
3
4
5
D(w),p(w)
5,u ∞
∞
1,u
2,u
u
8 Loop
9
10
add a to N'
ux
v w x y z
u
y
x
w
v
z
2
2
1
3
1
1
2
5
3
5
∞
2,x
4,x
2,u
uxy 4,y
3,y
2,u
uxyv 4,y
3,y
uxyvw

D(b) = min ( D(b), D(a) + ca,b )
D(z) = min ( D(z), D(w) + cw,z ) = min (4, 3+5) = 4
Step
0
1
2
3
4
5
D(w),p(w)
5,u ∞
∞
1,u
2,u
u
8 Loop
9
10
11
add a to N'
ux
v w x y z
u
y
x
w
v
z
2
2
1
3
1
1
2
5
3
5
∞
2,x
4,x
2,u
uxy 4,y
3,y
2,u
uxyv 4,y
3,y
uxyvw 4,y

Step
0
1
2
3
4
5
D(w),p(w)
5,u ∞
∞
1,u
2,u
u
8 Loop
9
10
add a to N'
ux
v w x y z
u
y
x
w
v
z
2
2
1
3
1
1
2
5
3
5
∞
2,x
4,x
2,u
uxy 4,y
3,y
2,u
uxyv 4,y
3,y
uxyvw 4,y
uxyvwz

Step
0
1
2
3
4
5
D(w),p(w)
5,u ∞
∞
1,u
2,u
u
8 Loop
9
10
11
add a to N'
ux
v w x y z
u
y
x
w
v
z
2
2
1
3
1
1
2
5
3
5
∞
2,x
4,x
2,u
uxy 4,y
3,y
2,u
uxyv 4,y
3,y
uxyvw 4,y
uxyvwz
D(b) = min ( D(b), D(a) + ca,b )

Network Layer: 5-27
u
y
x
w
v
z
2
2
1
3
1
1
2
5
3
5
u
y
x
w
v
z
resulting least-cost-path tree from u: resulting forwarding table in u:
v
x
y
w
x
(u,v)
(u,x)
(u,x)
(u,x)
(u,x)
destination outgoing link
route from u to v directly
route from u to all
other destinations
via x

Dijkstra’s algorithm: another example
Network Layer: 5-28
w
3
4
v
x
u
5
3
7 4
y
8
z
2
7
9
Step N'
D(v),
p(v)
0
1
2
3
4
5
D(w),
p(w)
D(x),
p(x)
D(y),
p(y)
D(z),
p(z)
u ∞
∞
7,u 3,u 5,u
uw ∞
11,w
6,w 5,u
14,x
11,w
6,w
uwx
uwxv 14,x
10,v
uwxvy 12,y
notes:
 construct least-cost-path tree by tracing predecessor nodes
 ties can exist (can be broken arbitrarily)
uwxvyz
v w x y z

Dijkstra’s algorithm: discussion
Network Layer: 5-29
algorithm complexity: n nodes
 each of n iteration: need to check all nodes, w, not in N
 n(n+1)/2 comparisons: O(n2
) complexity
 more efficient implementations possible: O(nlogn)
message complexity:
 each router must broadcast its link state information to other n routers
 efficient (and interesting!) broadcast algorithms: O(n) link crossings to disseminate a
broadcast message from one source
 each router’s message crosses O(n) links: overall message complexity: O(n2
)

Dijkstra’s algorithm: oscillations possible
Network Layer: 5-30
 when link costs depend on traffic volume, route oscillations possible
a
d
c
b
1 1+e
e
0
e
1
1
0 0
initially
a
d
c
b
given these costs,
find new routing….
resulting in new costs
2+e 0
0
0
1+e 1
a
d
c
b
given these costs,
0 2+e
1+e
1
0 0
a
d
c
b
given these costs,
2+e 0
0
0
1+e 1
 sample scenario:
• routing to destination a, traffic entering at d, c, e with rates 1, e (<1), 1
• link costs are directional, and volume-dependent
e
1 1
e
1 1
e
1 1

configuration
• SNMP
• NETCONF/YANG
 introduction
 link state
 distance vector
Protocol
Network Layer: 5-31

Based on Bellman-Ford (BF) equation (dynamic programming):
Distance vector algorithm
Network Layer: 5-32
Let Dx(y): cost of least-cost path from x to y.
Then:
Dx(y) = minv { cx,v + Dv(y) }
Bellman-Ford equation
min taken over all neighbors v of x
v’s estimated least-cost-path cost to y
direct cost of link from x to v

Bellman-Ford Example
Network Layer: 5-33
u
y
z
2
2
1
3
1
1
2
5
3
5
Suppose that u’s neighboring nodes, x,v,w, know that for destination z:
Du(z) = min { cu,v + Dv(z),
cu,x + Dx(z),
cu,w + Dw(z) }
Bellman-Ford equation says:
Dv(z) = 5
v
Dw(z) = 3
w
Dx(z) = 3
x
= min {2 + 5,
1 + 3,
5 + 3} = 4
node achieving minimum (x) is
next hop on estimated least-
cost path to destination (z)

Distance vector algorithm
Network Layer: 5-34
key idea:
 from time-to-time, each node sends its own distance vector estimate to
neighbors
 under minor, natural conditions, the estimate Dx
(y) converge to the
actual least cost dx(y)
Dx
(y) ← minv
{cx,v + Dv
(y)} for each node y ∊ N
 when x receives new DV estimate from any neighbor, it updates its
own DV using B-F equation:

Distance vector algorithm:
Network Layer: 5-35
iterative, asynchronous: each local
iteration caused by:
 local link cost change
 DV update message from neighbor
wait for (change in local link
cost or msg from neighbor)
each node:
distributed, self-stopping: each
node notifies neighbors only when
its DV changes
 neighbors then notify their
neighbors – only if necessary
 no notification received, no
actions taken!
recompute DV estimates using
DV received from neighbor
if DV to any destination has
changed, notify neighbors

DV in a:
Da(a)=0
Da(b) = 8
Da(c) = ∞
Da(d) = 1
Da(e) = ∞
Da(f) = ∞
Da(g) = ∞
Da(h) = ∞
Da(i) = ∞
Distance vector: example
Network Layer: 5-36
g h i
1 1
1 1 1
1 1
1 1
8 1
t=0
 All nodes have
distance estimates
to nearest
neighbors (only)
A few asymmetries:
 missing link
 larger cost
d e f
a b c
 All nodes send
their local
distance vector to
their neighbors

Distance vector example: iteration
Network Layer: 5-37
All nodes:
 receive distance
vectors from
neighbors
 compute their new
local distance
vector
 send their new
local distance
vector to neighbors
t=1
g h i
1 1
1 1 1
1 1
1 1
8 1
d e f
a b c

Network Layer: 5-38
g h i
1 1
1 1 1
1 1
1 1
8 1
d e f
a b c
All nodes:
vectors from
neighbors
local distance
vector
 send their new
local distance
vector to neighbors
t=1
compute compute compute

Network Layer: 5-39
g h i
1 1
1 1 1
1 1
1 1
8 1
d e f
a b c
All nodes:
vectors from
neighbors
local distance
vector
 send their new
local distance
vector to neighbors
t=1

Network Layer: 5-40
g h i
1 1
1 1 1
1 1
1 1
8 1
d e f
a b c
All nodes:
vectors from
neighbors
local distance
vector
 send their new
local distance
vector to neighbors
t=2

Network Layer: 5-41
g h i
1 1
1 1 1
1 1
8 1
2 1
d e f
a b c
All nodes:
vectors from
neighbors
local distance
vector
 send their new
local distance
vector to neighbors
t=2

Network Layer: 5-42
g h i
1 1
1 1 1
1 1
1 1
8 1
d e f
a b c
All nodes:
vectors from
neighbors
local distance
vector
 send their new
local distance
vector to neighbors
t=2

Network Layer: 5-43
…. and so on
Let’s next take a look at the iterative computations at nodes

DV in a:
Da(a)=0
Da(b) = 8
Da(c) = ∞
Da(d) = 1
Da(e) = ∞
Da(f) = ∞
Da(g) = ∞
Da(h) = ∞
Da(i) = ∞
Distance vector example: computation
Network Layer: 5-44
g h i
1 1
1 1 1
1 1
1 1
8 1
t=1
DV in b:
Db(f) = ∞
Db(g) = ∞
Db(h) = ∞
Db(i) = ∞
Db(a) = 8
Db(c) = 1
Db(d) = ∞
Db(e) = 1
 b receives DVs
from a, c, e
a b c
d e f
DV in c:
Dc(a) = ∞
Dc(b) = 1
Dc(c) = 0
Dc(d) = ∞
Dc(e) = ∞
Dc(f) = ∞
Dc(g) = ∞
Dc(h) = ∞
Dc(i) = ∞
DV in e:
De(a) = ∞
De(b) = 1
De(c) = ∞
De(d) = 1
De(e) = 0
De(f) = 1
De(g) = ∞
De(h) = 1
De(i) = ∞

DV in a:
Da(a)=0
Da(b) = 8
Da(c) = ∞
Da(d) = 1
Da(e) = ∞
Da(f) = ∞
Da(g) = ∞
Da(h) = ∞
Da(i) = ∞
DV in b:
Db(f) = ∞
Db(g) = ∞
Db(h) = ∞
Db(i) = ∞
Db(a) = 8
Db(c) = 1
Db(d) = ∞
Db(e) = 1
DV in c:
Dc(a) = ∞
Dc(b) = 1
Dc(c) = 0
Dc(d) = ∞
Dc(e) = ∞
Dc(f) = ∞
Dc(g) = ∞
Dc(h) = ∞
Dc(i) = ∞
DV in e:
De(a) = ∞
De(b) = 1
De(c) = ∞
De(d) = 1
De(e) = 0
De(f) = 1
De(g) = ∞
De(h) = 1
De(i) = ∞
Network Layer: 5-45
g h i
1 1
1 1 1
1 1
1 1
8 1
t=1
 b receives DVs
from a, c, e,
computes:
a b c
d e f
DV in b:
Db(f) =2
Db(g) = ∞
Db(h) = 2
Db(i) = ∞
Db(a) = 8
Db(c) = 1
Db(d) = 2
Db(e) = 1
e
compute
b
Db(a) = min{cb,a+Da(a), cb,c +Dc(a), cb,e+De(a)} = min{8,∞,∞} = 8
Db(c) = min{cb,a+Da(c), cb,c +Dc(c), cb,e +De(c)} = min{∞,1,∞} = 1
Db(d) = min{cb,a+Da(d), cb,c +Dc(d), cb,e +De(d)} = min{9,2,∞} = 2
Db(f) = min{cb,a+Da(f), cb,c +Dc(f), cb,e +De(f)} = min{∞,∞,2} = 2
Db(i) = min{cb,a+Da(i), cb,c +Dc(i), cb,e+De(i)} = min{∞,∞, ∞} = ∞
Db(h) = min{cb,a+Da(h), cb,c +Dc(h), cb,e+De(h)} = min{∞,∞, 2} = 2
Db(e) = min{cb,a+Da(e), cb,c +Dc(e), cb,e +De(e)} = min{∞,∞,1} = 1
Db(g) = min{cb,a+Da(g), cb,c +Dc(g), cb,e+De(g)} = min{∞,∞, ∞} = ∞

DV in a:
Da(a)=0
Da(b) = 8
Da(c) = ∞
Da(d) = 1
Da(e) = ∞
Da(f) = ∞
Da(g) = ∞
Da(h) = ∞
Da(i) = ∞
Network Layer: 5-46
g h i
1 1
1 1 1
1 1
1 1
8 1
t=1
DV in b:
Db(f) = ∞
Db(g) = ∞
Db(h) = ∞
Db(i) = ∞
Db(a) = 8
Db(c) = 1
Db(d) = ∞
Db(e) = 1
 c receives DVs
from b
a b c
d e f
DV in c:
Dc(a) = ∞
Dc(b) = 1
Dc(c) = 0
Dc(d) = ∞
Dc(e) = ∞
Dc(f) = ∞
Dc(g) = ∞
Dc(h) = ∞
Dc(i) = ∞
DV in e:
De(a) = ∞
De(b) = 1
De(c) = ∞
De(d) = 1
De(e) = 0
De(f) = 1
De(g) = ∞
De(h) = 1
De(i) = ∞

Network Layer: 5-47
g h i
1 1
8 1
t=1
DV in b:
Db(f) = ∞
Db(g) = ∞
Db(h) = ∞
Db(i) = ∞
Db(a) = 8
Db(c) = 1
Db(d) = ∞
Db(e) = 1
 c receives DVs
from b computes:
a b c
d e f
DV in c:
Dc(a) = ∞
Dc(b) = 1
Dc(c) = 0
Dc(d) = ∞
Dc(e) = ∞
Dc(f) = ∞
Dc(g) = ∞
Dc(h) = ∞
Dc(i) = ∞
Dc(a) = min{cc,b+Db(a}} = 1 + 8 = 9
Dc(b) = min{cc,b+Db(b)} = 1 + 0 = 1
Dc(d) = min{cc,b+Db(d)} = 1+ ∞ = ∞
Dc(e) = min{cc,b+Db(e)} = 1 + 1 = 2
Dc(f) = min{cc,b+Db(f)} = 1+ ∞ = ∞
Dc(g) = min{cc,b+Db(g)} = 1+ ∞ = ∞
Dc(i) = min{cc,b+Db(i)} = 1+ ∞ = ∞
Dc(h) = min{cbc,b+Db(h)} = 1+ ∞ = ∞
DV in c:
Dc(a) = 9
Dc(b) = 1
Dc(c) = 0
Dc(d) = 2
Dc(e) = ∞
Dc(f) = ∞
Dc(g) = ∞
Dc(h) = ∞
Dc(i) = ∞
compute
* Check out the online interactive
exercises for more examples:
http://gaia.cs.umass.edu/kurose_ross/interactive/

Network Layer: 5-48
1 1
1 1 1
1 1
1 1
8 1
t=1
DV in b:
Db(f) = ∞
Db(g) = ∞
Db(h) = ∞
Db(i) = ∞
Db(a) = 8
Db(c) = 1
Db(d) = ∞
Db(e) = 1
 e receives DVs
from b, d, f, h
a b c
DV in f:
Dc(a) = ∞
Dc(b) = ∞
Dc(c) = ∞
Dc(d) = ∞
Dc(e) = 1
Dc(f) = 0
Dc(g) = ∞
Dc(h) = ∞
Dc(i) = 1
DV in e:
De(a) = ∞
De(b) = 1
De(c) = ∞
De(d) = 1
De(e) = 0
De(f) = 1
De(g) = ∞
De(h) = 1
De(i) = ∞
DV in h:
Dc(a) = ∞
Dc(b) = ∞
Dc(c) = ∞
Dc(d) = ∞
Dc(e) = 1
Dc(f) = ∞
Dc(g) = 1
Dc(h) = 0
DV in d:
Dc(a) = 1
Dc(b) = ∞
Dc(c) = ∞
Dc(d) = 0
Dc(e) = 1
Dc(f) = ∞
Dc(g) = 1
Dc(h) = ∞
Dc(i) = ∞ d e f
g h i
Q: what is new DV computed in e at
t=1?
compute

Distance vector: state information diffusion
t=0 c’s state at t=0 is at c only
g h i
1 1
1 1 1
1 1
1 1
8 1
d e f
a b c
c’s state at t=0 has propagated to b, and
may influence distance vector computations
up to 1 hop away, i.e., at b
t=1
c’s state at t=0 may now influence distance
vector computations up to 2 hops away, i.e.,
at b and now at a, e as well
t=2
c’s state at t=0 may influence distance vector
computations up to 3 hops away, i.e., at d, f, h
t=3
c’s state at t=0 may influence distance vector
computations up to 4 hops away, i.e., at g, i
t=4
Iterative communication, computation steps diffuses information through network:
t=1
t=2
t=3
t=4

Distance vector: link cost changes
“good news
travels fast”
t0 : y detects link-cost change, updates its DV, informs its neighbors.
t1 : z receives update from y, updates its DV, computes new least cost
to x , sends its neighbors its DV.
t2 : y receives z’s update, updates its DV. y’s least costs do not
change, so y does not send a message to z.
link cost changes:
 node detects local link cost change
 updates routing info, recalculates local DV
 if DV changes, notify neighbors
x z
1
4
50
y
1

Distance vector: link cost changes
link cost changes:
 node detects local link cost change
 “bad news travels slow” – count-to-infinity problem:
x z
1
4
50
y
60
• y sees direct link to x has new cost 60, but z has said it has a path at cost of 5. So
y computes “my new cost to x will be 6, via z); notifies z of new cost of 6 to x.
• z learns that path to x via y has new cost 6, so z computes “my new cost to
x will be 7 via y), notifies y of new cost of 7 to x.
• y learns that path to x via z has new cost 7, so y computes “my new cost to
x will be 8 via y), notifies z of new cost of 8 to x.
• z learns that path to x via y has new cost 8, so z computes “my new cost to
x will be 9 via y), notifies y of new cost of 9 to x.
…
 see text for solutions. Distributed algorithms are tricky!

Comparison of LS and DV algorithms
message complexity
LS: n routers, O(n2
) messages sent
DV: exchange between neighbors;
convergence time varies
speed of convergence
LS: O(n2
) algorithm, O(n2
) messages
• may have oscillations
DV: convergence time varies
• may have routing loops
• count-to-infinity problem
robustness: what happens if router
malfunctions, or is compromised?
LS:
• router can advertise incorrect link cost
• each router computes only its own
table
DV:
• DV router can advertise incorrect path
cost (“I have a really low-cost path to
everywhere”): black-holing
• each router’s DV is used by others:
error propagate thru network

configuration
• SNMP
• NETCONF/YANG
 introduction
Protocol
Network Layer: 5-53

our routing study thus far - idealized
 all routers identical
 network “flat”
… not true in practice
Making routing scalable
Network Layer: 5-54
scale: billions of destinations:
 can’t store all destinations in
routing tables!
 routing table exchange would
swamp links!
administrative autonomy:
 Internet: a network of networks
 each network admin may want to
control routing in its own network

aggregate routers into regions known as “autonomous
systems” (AS) (a.k.a. “domains”)
Internet approach to scalable routing
Network Layer: 5-55
intra-AS (aka “intra-domain”):
routing among routers within same
AS (“network”)
 all routers in AS must run same intra-
domain protocol
 routers in different AS can run different
intra-domain routing protocols
 gateway router: at “edge” of its own AS,
has link(s) to router(s) in other AS’es
inter-AS (aka “inter-domain”):
routing among AS’es
 gateways perform inter-domain
routing (as well as intra-domain
routing)

Interconnected ASes
Network Layer: 5-56
3b
1d
3a
1c
2a
AS3
AS1
AS2
1a
2c
2b
1b
3c
intra-AS
routing
intra-AS
routing
intra-AS
routing
inter-AS routing
forwarding
table
forwarding table configured by intra-
and inter-AS routing algorithms
Intra-AS
Routing
Inter-AS
Routing  intra-AS routing determine entries for
destinations within AS
 inter-AS & intra-AS determine entries
for external destinations

Inter-AS routing: a role in intradomain forwarding
Network Layer: 5-57
3b
1d
3a
1c
2a
AS3
AS1
AS2
1a
2c
2b
1b
3c
other
networks
other
networks
 suppose router in AS1 receives
datagram destined outside of AS1:
AS1 inter-domain routing must:
1. learn which destinations reachable
through AS2, which through AS3
2. propagate this reachability info to all
routers in AS1
• router should forward packet to
gateway router in AS1, but which
one?

Intra-AS routing: routing within an AS
Network Layer: 5-58
most common intra-AS routing protocols:
 RIP: Routing Information Protocol [RFC 1723]
• classic DV: DVs exchanged every 30 secs
• no longer widely used
 EIGRP: Enhanced Interior Gateway Routing Protocol
• DV based
• formerly Cisco-proprietary for decades (became open in 2013 [RFC 7868])
 OSPF: Open Shortest Path First [RFC 2328]
• link-state routing
• IS-IS protocol (ISO standard, not RFC standard) essentially same as OSPF

OSPF (Open Shortest Path First) routing
Network Layer: 5-59
 “open”: publicly available
 classic link-state
• each router floods OSPF link-state advertisements (directly over IP
rather than using TCP/UDP) to all other routers in entire AS
• multiple link costs metrics possible: bandwidth, delay
• each router has full topology, uses Dijkstra’s algorithm to compute
forwarding table
 security: all OSPF messages authenticated (to prevent malicious
intrusion)

Hierarchical OSPF
Network Layer: 5-60
 two-level hierarchy: local area, backbone.
• link-state advertisements flooded only in area, or backbone
• each node has detailed area topology; only knows direction to reach
other destinations
area border routers:
“summarize” distances to
destinations in own area,
advertise in backbone
area 1
area 2
area 3
backbone
internal
routers
backbone router:
runs OSPF limited
to backbone
boundary router:
connects to other ASes
local routers:
• flood LS in area only
• compute routing within
area
• forward packets to outside
via area border router

configuration
• SNMP
• NETCONF/YANG
 introduction
Protocol
Network Layer: 5-61

Interconnected ASes
3b
1d
3a
1c
2a
AS3
AS1
AS2
1a
2c
2b
1b
3c
intra-AS
routing
intra-AS
routing
intra-AS
routing
inter-AS routing
intra-AS (aka “intra-domain”): routing among routers within same
AS (“network”)
inter-AS (aka “inter-domain”): routing among AS’es
Network Layer Control Plane: 5-62

 BGP (Border Gateway Protocol): the de facto inter-domain routing
protocol
• “glue that holds the Internet together”
 allows subnet to advertise its existence, and the destinations it can
reach, to rest of Internet: “I am here, here is who I can reach, and how”
 BGP provides each AS a means to:
• obtain destination network reachability info from neighboring ASes
(eBGP)
• determine routes to other networks based on reachability information
and policy
• propagate reachability information to all AS-internal routers (iBGP)
• advertise (to neighboring networks) destination reachability info
Internet inter-AS routing: BGP
Network Layer Control Plane: 5-63

eBGP, iBGP connections
Network Layer: 5-64
eBGP connectivity
logical iBGP connectivity
1b
1d
1c
1a
2b
2d
2c
2a
3b
3d
3c
3a
AS 2
AS 3
AS 1
1c
∂
∂
gateway routers run both eBGP and iBGP protocols

BGP basics
Network Layer: 5-65
 when AS3 gateway 3a advertises path AS3,X to AS2 gateway 2c:
• AS3 promises to AS2 it will forward datagrams towards X
 BGP session: two BGP routers (“peers”) exchange BGP messages over
semi-permanent TCP connection:
• advertising paths to different destination network prefixes (BGP is a “path
vector” protocol)
2b
2d
2c
2a
AS 2
3b
3d
3c
3a
AS 3
1b
1d
1c
1a
AS 1
X
BGP advertisement:
AS3, X

BGP protocol messages
 BGP messages exchanged between peers over TCP connection
 BGP messages [RFC 4371]:
• OPEN: opens TCP connection to remote BGP peer and authenticates
sending BGP peer
• UPDATE: advertises new path (or withdraws old)
• KEEPALIVE: keeps connection alive in absence of UPDATES; also ACKs
OPEN request
• NOTIFICATION: reports errors in previous msg; also used to close
connection

Path attributes and BGP routes
Network Layer: 5-67
 BGP advertised route: prefix + attributes
• prefix: destination being advertised
• two important attributes:
• AS-PATH: list of ASes through which prefix advertisement has passed
• NEXT-HOP: indicates specific internal-AS router to next-hop AS
 policy-based routing:
• gateway receiving route advertisement uses import policy to
accept/decline path (e.g., never route through AS Y).
• AS policy also determines whether to advertise path to other other
neighboring ASes

2b
2d
2c
2a
AS 2
3b
3d
3c
3a
AS 3
1b
1d
1c
1a
AS 1
X
BGP path advertisement
Network Layer: 5-68
 based on AS2 policy, AS2 router 2c accepts path AS3,X, propagates (via iBGP) to all
AS2 routers
AS2,AS3,X
 AS2 router 2c receives path advertisement AS3,X (via eBGP) from AS3 router 3a
 based on AS2 policy, AS2 router 2a advertises (via eBGP) path AS2, AS3, X to
AS1 router 1c
AS3, X

Network Layer: 5-69
AS2,AS3,X
 AS1 gateway router 1c learns path AS2,AS3,X from 2a
gateway router may learn about multiple paths to destination:
AS3,X
 AS1 gateway router 1c learns path AS3,X from 3a
 based on policy, AS1 gateway router 1c chooses path AS3,X and advertises path
within AS1 via iBGP
AS3, X
2b
2d
2c
2a
AS 2
3b
3d
3c
3a
AS 3
1b
1d
1c
1a
AS 1
X
AS3,X
AS3,X
AS3,X
BGP path advertisement: multiple paths

2b
2d
2c
2a
AS 2
3b
3d
3c
3a
AS 3
1b
1d
1c
1a
AS 1
X
BGP: populating forwarding tables
AS2,AS3,X
AS3,X
AS3, X
 recall: 1a, 1b, 1d learn via iBGP from 1c: “path to X goes through 1c”
 at 1d: OSPF intra-domain routing: to get to 1c, use interface 1
1
2
1
2
dest interface
…
…
…
…
local link
interfaces
at 1a, 1d
 at 1d: to get to X, use interface 1
1c 1
X 1
AS3,X
AS3,X
AS3,X

2b
2d
2c
2a
AS 2
3b
3d
3c
3a
AS 3
1b
1d
1c
1a
AS 1
X
BGP: populating forwarding tables
 recall: 1a, 1b, 1d learn via iBGP from 1c: “path to X goes through 1c”
 at 1d: OSPF intra-domain routing: to get to 1c, use interface 1
1
2
 at 1d: to get to X, use interface 1
dest interface
…
…
…
…
1c 2
X 2
 at 1a: OSPF intra-domain routing: to get to 1c, use interface 2
 at 1a: to get to X, use interface 2

2b
2d
2c
2a
AS 2
3b
3d
3c
3a
AS 3
1b
1d
1c
1a
AS 1
X
Hot potato routing
Network Layer: 5-72
 2d learns (via iBGP) it can route to X via 2a or 2c
 hot potato routing: choose local gateway that has least intra-domain
cost (e.g., 2d chooses 2a, even though more AS hops to X): don’t worry
about inter-domain cost!
AS3,X
AS1,AS3,X
OSPF link weights
201
112
263

BGP: achieving policy via advertisements
Network Layer: 5-73
B
legend:
customer
network:
provider
network
 A advertises path Aw to B and to C
 B chooses not to advertise BAw to C!
 B gets no “revenue” for routing CBAw, since none of C, A, w are B’s customers
 C does not learn about CBAw path
 C will route CAw (not using B) to get to w
ISP only wants to route traffic to/from its customer networks (does not want
to carry transit traffic between other ISPs – a typical “real world” policy)
w A
y
C
x
A,w
A,w

BGP: achieving policy via advertisements (more)
Network Layer: 5-74
B
ISP only wants to route traffic to/from its customer networks (does not want
to carry transit traffic between other ISPs – a typical “real world” policy)
w A
y
C
x
 A,B,C are provider networks
 x,w,y are customer (of provider networks)
 x is dual-homed: attached to two networks
 policy to enforce: x does not want to route from B to C via x
 .. so x will not advertise to B a route to C
legend:
customer
network:
provider
network

 router may learn about more than one route to destination
AS, selects route based on:
1. local preference value attribute: policy decision
2. shortest AS-PATH
3. closest NEXT-HOP router: hot potato routing
4. additional criteria
BGP route selection
Network Layer: 5-75

Why different Intra-, Inter-AS routing ?
Network Layer: 5-76
policy:
 inter-AS: admin wants control over how its traffic routed, who
routes through its network
 intra-AS: single admin, so policy less of an issue
scale:
 hierarchical routing saves table size, reduced update traffic
performance:
 intra-AS: can focus on performance
 inter-AS: policy dominates over performance

configuration
• SNMP
• NETCONF/YANG
 introduction
Protocol
Network Layer: 5-77

 Internet network layer: historically implemented via
distributed, per-router control approach:
• monolithic router contains switching hardware, runs proprietary
implementation of Internet standard protocols (IP, RIP, IS-IS, OSPF,
BGP) in proprietary router OS (e.g., Cisco IOS)
• different “middleboxes” for different network layer functions:
firewalls, load balancers, NAT boxes, ..
 ~2005: renewed interest in rethinking network control plane
Software defined networking (SDN)
Network Layer: 5-78

Per-router control plane
Individual routing algorithm components in each and every router
interact in the control plane to computer forwarding tables
Routing
Algorithm
data
plane
control
plane
1
2
0111
values in arriving
packet header
3
Network Layer: 4-79

Software-Defined Networking (SDN) control plane
Remote controller computes, installs forwarding tables in routers
data
plane
control
plane
Remote Controller
CA
CA CA CA CA
1
2
0111
3
values in arriving
packet header
Network Layer: 4-80

Why a logically centralized control plane?
 easier network management: avoid router misconfigurations,
greater flexibility of traffic flows
 table-based forwarding (recall OpenFlow API) allows
“programming” routers
• centralized “programming” easier: compute tables centrally and distribute
• distributed “programming” more difficult: compute tables as result of
distributed algorithm (protocol) implemented in each-and-every router
 open (non-proprietary) implementation of control plane
• foster innovation: let 1000 flowers bloom
Network Layer: 5-81

SDN analogy: mainframe to PC revolution
Network Layer: 5-82
Vertically integrated
Closed, proprietary
Slow innovation
Small industry
Specialized
Operating
System
Specialized
Hardware
Ap
p
Ap
p
Ap
p
Ap
p
Ap
p
Ap
p
Ap
p
Ap
p
Ap
p
Ap
p
App
Specialized
Applications
Horizontal
Open interfaces
Rapid innovation
Huge industry
Microprocessor
Open Interface
* Slide courtesy: N. McKeown
or or
Open Interface
Windows Linux MAC OS

2
2
1
3
1
1
2
5
3
5
v w
u z
y
x
Traffic engineering: difficult with traditional routing
Network Layer: 5-83
Q: what if network operator wants u-to-z traffic to flow along
uvwz, rather than uxyz?
A: need to re-define link weights so traffic routing algorithm
computes routes accordingly (or need a new routing algorithm)!
link weights are only control “knobs”: not much control!

2
2
1
3
1
1
2
5
3
5
v w
u z
y
x
Network Layer: 5-84
Q: what if network operator wants to split u-to-z
traffic along uvwz and uxyz (load balancing)?
A: can’t do it (or need a new routing algorithm)

Network Layer: 5-85
Q: what if w wants to route blue and red traffic differently from w to z?
A: can’t do it (with destination-based forwarding, and LS, DV routing)
2
2
1
3
1
1
2
5
3
5
v w
u z
y
x
We learned in Chapter 4 that generalized forwarding and SDN can
be used to achieve any routing desired

Network Layer: 5-86
data
plane
control
plane
Remote Controller
CA
CA CA CA CA
1: generalized “flow-based”
forwarding (e.g., OpenFlow)
2. control, data plane
separation
3. control plane functions
external to data-plane
switches
…
routing
access
control
load
balance
4. programmable
control
applications

Network Layer: 5-87
Data-plane switches:
 fast, simple, commodity switches
implementing generalized data-plane
forwarding (Section 4.4) in hardware
 flow (forwarding) table computed,
installed under controller supervision
 API for table-based switch control
(e.g., OpenFlow)
• defines what is controllable, what is not
 protocol for communicating with
controller (e.g., OpenFlow)
data
plane
control
plane
SDN Controller
(network operating system)
…
routing
access
control
load
balance
southbound API
northbound API
SDN-controlled switches
network-control
applications

Network Layer: 5-88
SDN controller (network OS):
 maintain network state
information
 interacts with network control
applications “above” via
northbound API
 interacts with network switches
“below” via southbound API
 implemented as distributed system
for performance, scalability, fault-
tolerance, robustness
data
plane
control
plane
SDN Controller
…
routing
access
control
load
balance
southbound API
northbound API
network-control
applications

Network Layer: 5-89
network-control apps:
 “brains” of control: implement
control functions using lower-
level services, API provided by
SDN controller
 unbundled: can be provided by
3rd
party: distinct from routing
vendor, or SDN controller
data
plane
control
plane
SDN Controller
…
routing
access
control
load
balance
southbound API
northbound API
network-control
applications

Components of SDN controller
Network Layer: 5-90
Network-wide distributed, robust state management
Communication to/from controlled devices
Link-state info switch info
host info
statistics flow tables
…
…
OpenFlow SNMP
…
network
graph intent
RESTful
API
…
Interface, abstractions for network control apps
SDN
controller
routing access
control
load
balance
communication: communicate
between SDN controller and
controlled switches
network-wide state
management : state of
networks links, switches,
services: a distributed database
interface layer to network
control apps: abstractions API

OpenFlow protocol
Network Layer: 5-91
 operates between controller, switch
 TCP used to exchange messages
• optional encryption
 three classes of OpenFlow messages:
• controller-to-switch
• asynchronous (switch to controller)
• symmetric (misc.)
 distinct from OpenFlow API
• API used to specify generalized
forwarding actions
OpenFlow Controller

OpenFlow: controller-to-switch messages
Network Layer: 5-92
Key controller-to-switch messages
 features: controller queries switch
features, switch replies
 configure: controller queries/sets
switch configuration parameters
 modify-state: add, delete, modify flow
entries in the OpenFlow tables
 packet-out: controller can send this
packet out of specific switch port
OpenFlow Controller

OpenFlow: switch-to-controller messages
Network Layer: 5-93
Key switch-to-controller messages
 packet-in: transfer packet (and its
control) to controller. See packet-out
message from controller
 flow-removed: flow table entry deleted
at switch
 port status: inform controller of a
change on a port.
Fortunately, network operators don’t “program” switches by creating/sending
OpenFlow messages directly. Instead use higher-level abstraction at controller
OpenFlow Controller

SDN: control/data plane interaction example
Network Layer: 5-94
host info
…
…
OpenFlow SNMP
…
network
graph intent
RESTful
API
…
Dijkstra’s link-state
routing
s1
s2
s3
s4
S1, experiencing link failure uses
OpenFlow port status message to
notify controller
1
SDN controller receives OpenFlow
message, updates link status info
2
Dijkstra’s routing algorithm
application has previously registered
to be called when ever link status
changes. It is called.
3
Dijkstra’s routing algorithm access
network graph info, link state info
in controller, computes new
routes
4
1
2
3
4

SDN: control/data plane interaction example
Network Layer: 5-95
host info
…
…
OpenFlow SNMP
…
network
graph intent
RESTful
API
…
Dijkstra’s link-state
routing
s1
s2
s3
s4
link state routing app interacts
with flow-table-computation
component in SDN controller,
which computes new flow tables
needed
5
controller uses OpenFlow to
install new tables in switches
that need updating
6
5
6
1
2
3
4

Google ORION SDN control plane
ORION: Google’s SDN control plane (NSDI’21): control plane for
Google’s datacenter (Jupiter) and wide area (B4) networks
Orion SDN architecture and core apps
 routing (intradomain, iBGP), traffic
engineering: implemented in applications
on top of ORION core
 edge-edge flow-based controls (e.g.,
CoFlow scheduling) to meet contract SLAs
 management: pub-sub distributed
microservices in Orion core, OpenFlow for
switch signaling/monitoring
Note: ORION provides intradomain services within Google’s network

OpenDaylight (ODL) controller
Network Layer: 5-97
Network Orchestrations and Applications
Southbound API
Service Abstraction
Layer (SAL)
config. and
operational data
store
REST/RESTCONF/NETCONF APIs
messaging
OpenFlow NETCONF SNMP OVSDB …
Northbound API
Traffic
Engineering …
Firewalling Load Balancing
Basic Network Functions
Enhanced
Services
…
…
Forwarding
rules mgr.
AAA
Host
Tracker
Stats
mgr.
Switch
mgr.
Topology
processing
Service Abstraction Layer:
 interconnects internal,
external applications
and services

ONOS controller
Network Layer: 5-98
Network Applications
Southbound API
Northbound API
Traffic
Engineering …
Firewalling Load Balancing
southbound
abstractions,
protocols
OpenFlow Netconf OVSDB
device link host flow packet
northbound
abstractions,
protocols
REST API Intent
ONOS
distributed
core
statistics
devices
hosts
links
paths flow rules topology
 control apps separate
from controller
 intent framework: high-
level specification of
service: what rather
than how
 considerable emphasis
on distributed core:
service reliability,
replication performance
scaling

 hardening the control plane: dependable, reliable, performance-
scalable, secure distributed system
• robustness to failures: leverage strong theory of reliable distributed
system for control plane
• dependability, security: “baked in” from day one?
 networks, protocols meeting mission-specific requirements
• e.g., real-time, ultra-reliable, ultra-secure
 Internet-scaling: beyond a single AS
 SDN critical in 5G cellular networks
SDN: selected challenges
Network Layer: 5-99

 SDN-computed versus router-computer forwarding tables:
• just one example of logically-centralized-computed versus protocol
computed
 one could imagine SDN-computed congestion control:
• controller sets sender rates based on router-reported (to
controller) congestion levels
SDN and the future of traditional network protocols
Network Layer: 5-100
How will implementation of
network functionality (SDN
versus protocols) evolve?

configuration
• SNMP
• NETCONF/YANG
 introduction
Protocol

ICMP: internet control message protocol
 used by hosts and routers to
communicate network-level
information
• error reporting: unreachable host,
network, port, protocol
• echo request/reply (used by ping)
 network-layer “above” IP:
• ICMP messages carried in IP
datagrams
 ICMP message: type, code plus first
8 bytes of IP datagram causing
error
Type Code description
0 0 echo reply (ping)
3 0 dest. network unreachable
3 1 dest host unreachable
3 2 dest protocol unreachable
3 3 dest port unreachable
3 6 dest network unknown
3 7 dest host unknown
4 0 source quench (congestion
control - not used)
8 0 echo request (ping)
9 0 route advertisement
10 0 router discovery
11 0 TTL expired
12 0 bad IP header

Traceroute and ICMP
 when ICMP message arrives at source: record RTTs
stopping criteria:
 UDP segment eventually
arrives at destination host
 destination returns ICMP
“port unreachable”
message (type 3, code 3)
 source stops
3 probes
3 probes
3 probes
 source sends sets of UDP segments to
destination
• 1st
set has TTL =1, 2nd
set has TTL=2, etc.
 datagram in nth set arrives to nth router:
• router discards datagram and sends source
ICMP message (type 11, code 0)
• ICMP message possibly includes name of
router & IP address

configuration
• SNMP
• NETCONF/YANG
 introduction
Protocol

 autonomous systems (aka “network”): 1000s of interacting
hardware/software components
 other complex systems requiring monitoring, configuration,
control:
• jet airplane, nuclear power plant, others?
What is network management?
"Network management includes the deployment, integration
and coordination of the hardware, software, and human
elements to monitor, test, poll, configure, analyze, evaluate,
and control the network and element resources to meet the
real-time, operational performance, and Quality of Service
requirements at a reasonable cost."

Components of network management
managed device
managed device
managed device
managed device
managed device
agent data
agent data
agent data
agent data
agent data
managing
server/controller
data
Managing server:
application, typically
with network
managers (humans) in
the loop
Managed device:
equipment with manageable,
configurable hardware,
software components
Data: device “state”
configuration data,
operational data,
device statistics
Network
management
protocol: used by
managing server to query,
configure, manage device;
used by devices to inform
managing server of data,
events.

Network operator approaches to management
managed device
managed device
managed device
managed device
managed device
agent data
agent data
agent data
agent data
agent data
managing
server/controller
data
CLI (Command Line Interface)
• operator issues (types, scripts) direct to
individual devices (e.g., vis ssh)
SNMP/MIB
• operator queries/sets devices data
(MIB) using Simple Network
Management Protocol (SNMP)
NETCONF/YANG
• more abstract, network-wide, holistic
• emphasis on multi-device configuration
management.
• YANG: data modeling language
• NETCONF: communicate YANG-compatible
actions/data to/from/among remote devices

SNMP protocol
managed device
agent data
managing
server/controller
data
request
response trap message
Two ways to convey MIB info, commands:
request/response mode
managed device
agent data
managing
server/controller
data
trap mode

SNMP protocol: message types
GetRequest
GetNextRequest
GetBulkRequest
manager-to-agent: “get me data”
(data instance, next data in list,
block of data).
Message type Function
SetRequest manager-to-agent: set MIB value
Response Agent-to-manager: value, response
to Request
Trap Agent-to-manager: inform manager
of exceptional event

SNMP protocol: message formats
….
PDU
type
(0-3)
Request
ID
Error
Status
(0-5)
Error
Index
Name Value Name Value
Get/set header Variables to get/set
SNMP PDU
message types 0-3
….
PDU
type
4
Enterprise Agent
Addr
Trap
Type
(0-7)
Specific
code
Time
stamp
Name Value
Trap header Trap info
message type 4

 managed device’s operational (and some configuration) data
 gathered into device MIB module
• 400 MIB modules defined in RFC’s; many more vendor-specific MIBs
SNMP: Management Information Base (MIB)
Object ID Name Type Comments
1.3.6.1.2.1.7.1 UDPInDatagrams 32-bit counter total # datagrams delivered
1.3.6.1.2.1.7.2 UDPNoPorts 32-bit counter # undeliverable datagrams (no application at port)
1.3.6.1.2.1.7.3 UDInErrors 32-bit counter # undeliverable datagrams (all other reasons)
1.3.6.1.2.1.7.4 UDPOutDatagrams 32-bit counter total # datagrams sent
1.3.6.1.2.1.7.5 udpTable SEQUENCE one entry for each port currently in use
agent data
 Structure of Management Information (SMI): data definition language
 example MIB variables for UDP protocol:

 goal: actively manage/configure devices network-wide
 operates between managing server and managed network devices
• actions: retrieve, set, modify, activate configurations
• atomic-commit actions over multiple devices
• query operational data and statistics
• subscribe to notifications from devices
 remote procedure call (RPC) paradigm
• NETCONF protocol messages encoded in XML
• exchanged over secure, reliable transport (e.g., TLS) protocol
NETCONF overview

NETCONF initialization, exchange, close
Session initiation,
capabilities exchange: <hello>
Session close: <close-session>
<rpc>
<rpc-reply>
<rpc>
<rpc-reply>
<rpc>
<rpc-reply>
<notification>
…
…
…
…
…
…
…
…
…
managing
server/controller
data
agent data

Selected NETCONF Operations
NETCONF Operation Description
<get-config> Retrieve all or part of a given configuration. A device may have multiple
configurations.
<get> Retrieve all or part of both configuration state and operational state data.
<edit-config> Change specified (possibly running) configuration at managed device.
Managed device <rpc-reply> contains <ok> or <rpcerror> with rollback.
<lock>, <unlock> Lock (unlock) configuration datastore at managed device (to lock out
NETCONF, SNMP, or CLIs commands from other sources).
<create-subscription>, Enable event notification subscription from managed device
<notification>

Sample NETCONF RPC message
note message id
change the running configuration
change MTU of Ethernet 0/0 interface to 1500
change a configuration

 data modeling language used to specify
structure, syntax, semantics of
NETCONF network management data
• built-in data types, like SMI
 XML document describing device,
capabilities can be generated from
YANG description
 can express constraints among data that
must be satisfied by a valid NETCONF
configuration
• ensure NETCONF configurations satisfy
correctness, consistency constraints
YANG
agent data
managing
server/controller
data
NETCONF RPC message
<edit-config>
YANG-generated XML
</edit-config> YANG
generated

Network layer: Summary
we’ve learned a lot!
 approaches to network control plane
• per-router control (traditional)
• logically centralized control (software defined networking)
 traditional routing algorithms
• implementation in Internet: OSPF , BGP
 SDN controllers
• implementation in practice: ODL, ONOS
 Internet Control Message Protocol
 network management
next stop: link layer!

Network layer, control plane: Done!
configuration
• SNMP
• NETCONF/YANG
introduction
 link state
 distance vector
Protocol

Additional Chapter 5 slides

Distance vector: another example
x y z
x
y
z
0 2 7
∞ ∞ ∞
∞ ∞ ∞
from
cost to
from
from x y z
x
y
z
0
x y z
x
y
z
∞ ∞
∞ ∞ ∞
cost to
x y z
x
y
z
∞ ∞ ∞
7 1 0
cost to
∞
2 0 1
∞ ∞ ∞
2 0 1
7 1 0
time
x z
1
2
7
y
Dx()
Dx(y) = min{cx,y + Dy(y), cx,z+ Dz(y)}
= min{2+0 , 7+1} = 2
Dx(z) = min{cx,y+ Dy(z), cx,z+ Dz(z)}
= min{2+1 , 7+0} = 3
3
2
Dy()
Dz()
cost to
from

Distance vector: another example
x y z
x
y
z
0 2 7
∞ ∞ ∞
∞ ∞ ∞
cost to
from
from
x y z
x
y
z
∞ ∞
∞ ∞ ∞
cost to
x y z
x
y
z
∞ ∞ ∞
7 1 0
cost to
∞
2 0 1
∞ ∞ ∞
x z
1
2
7
y
Dx()
Dy()
Dz()
from x y z
x
y
z
0 2 3
from
cost to
x y z
x
y
z
0 2 7
from
cost to
x y z
x
y
z
0 2 3
from
cost to
x y z
x
y
z
0 2 3
from
cost to
x y z
x
y
z
0 2 7
from
cost to
2 0 1
7 1 0
2 0 1
3 1 0
2 0 1
3 1 0
2 0 1
3 1 0
2 0 1
3 1 0
from
x y z
x
y
z
0
2 0 1
7 1 0
3
2
cost to
time

Network Layer: Control Plane (Computer Network Course)

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