Chapter14

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CEN 5501C
-

Computer Networks
-

Spring 2007
-

UF/CISE
-

Newman

1

Computer Networks

Chapter 14


Specific Routing Protocols

CEN 5501C
-

Computer Networks
-

Spring 2007
-

UF/CISE
-

Newman

2

Routing Protocols


Distance Vector


RIP (IP, IPX) (Routing Information Protocol)


RTMP (AppleTalk) (Routing Table Maintenance Prot.)


DECnet Phases 3 and 4


EGP (IP interdomain) (Exterior Gateway Protocol)


BGP (IP interdomain) (Border Gateway Protocol)


Link State


IS
-
IS (IP, CLNP) (Intermediate System
-
to
-
IS)


NLSP (IPX) (NetWare Link Services Protocol)


OSPF (IP) (Open Shortest Path First)


PNNI (ATM) (Private Network
-
to
-
Network Interface)

CEN 5501C
-

Computer Networks
-

Spring 2007
-

UF/CISE
-

Newman

3

History


DV


earliest routing protocols:


DECnet, “old” ARPANET, RIP


LS followed


ARPANET “new” (ca. 1980)


DECnet Phase V (ca. 1985)


IS
-
IS (based on DECnet V, ca. 1988)


OSPF (NIH syndrome at IETF, ca. ’89,’91,…)


Interdomain (DV):


GGP (manual configuration!, ca. 1979)


EGP (ca. 1982)


BGP (ca. 1989,1990, BGP
-
3 1991, BGP
-
4 1995)

CEN 5501C
-

Computer Networks
-

Spring 2007
-

UF/CISE
-

Newman

4

Interior vs. Exterior Gateways


Interior Gateways (routers)


Under same administration (same AS)


Run single interior gateway protocol


Typically RIP, OSPF, IS
-
IS, etc.


Exterior Gateways (border routers)


Connect Autonomous Systems (AS)


Run exterior gateway protocol with other EGs


Run IGP with IGs in same AS


Typically BGP
-
4


CEN 5501C
-

Computer Networks
-

Spring 2007
-

UF/CISE
-

Newman

5

RIP


Routing Information Protocol


For Interior Gateways (routers)


DV protocol


Specified in RFC 1058 after deployment!


RIP
-
2


Added authentication


Added masks, ability to advertise by proxy


Aging


Report distances at least every 30 sec.


Discard after 180 seconds of age


CEN 5501C
-

Computer Networks
-

Spring 2007
-

UF/CISE
-

Newman

6

RIP v1

Command (1)

Version (1)

Reserved (2)

Addr Fam ID (2)

Address (14)

Metric (4)

Repeated

Command (1)

Version (1)

Reserved (2)

0x0002

Metric (4)

Repeated

Reserved (2)

IP Address (4)

Reserved (8)

RIP v1

RIP v1 as used with IP

Up to 25 DV entries

Slow to converge (long timeouts)

High overhead (Tx all routing info every 30 sec.)

CEN 5501C
-

Computer Networks
-

Spring 2007
-

UF/CISE
-

Newman

7

RIP v2 with Authentication

Command (1)

Version=2 (1)

Reserved (2)

Addr Fam=0xFFFF

IP Address (4)

Metric (4)

Repeated

RFC 2453


Command


1=request


2=response

Address Family=0xFFFF


indicates authentication

Authentication Type and Info for security


use Hash Type and Hash Value

Route Tag … watch this space…

Mask for CIDR

Next Hop used for proxy adverts


= 0 if info for self, or


not 0 for another router on LAN

Auth Type (2)

Auth Info (16)

Addr Fam Ind=0x0002

Route Tag (2)

Mask (4)

Next Hop (4)

CEN 5501C
-

Computer Networks
-

Spring 2007
-

UF/CISE
-

Newman

8

RTMP, IPX
-
RIP, DECnet


RTMP, IPX
-
RIP


Similar to RIP


RTMP


report 10 sec/discard 20 sec!


Mandate split horizon


IPX
-
RIP requires triggered updates, PR


Dual Metrics used by IPX
-
RIP and DECnet


DECnet


Specific information sent reliably (not periodic)


Separate Hello messages for liveness


Store DVs from all nbors


fast recompute

CEN 5501C
-

Computer Networks
-

Spring 2007
-

UF/CISE
-

Newman

9

IS
-
IS, OSPF, NLSP, PNNI


Mostly the same


Self
-
stabilized flooding, LAN use from IS
-
IS


Hierarchical


OSPF allows 2 levels


IS
-
IS is multilevel tree hierarchy


Both now allow tradeoffs for route optimality
vs. routing information quantity


NLSP, PNNI allow arbitrary meshes

CEN 5501C
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Computer Networks
-

Spring 2007
-

UF/CISE
-

Newman

10

NLSP Area Connection

Area A

R

Area B

LSP from B

Only sent to B

LSP from A

Only sent to A


Filtering


decides addr import/export


Summarization


addr prefixes, distances

p1

p2

p3

Summary from A injected


into LSPs for B;

Summary from B injected


into LSPs for A

CEN 5501C
-

Computer Networks
-

Spring 2007
-

UF/CISE
-

Newman

11

OSPF Hierarchy

Area A

Area B


Strict 2
-
level hierarchy


Inter
-
area traffic must go through backbone

Backbone

E

F

C

D

G

CEN 5501C
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Computer Networks
-

Spring 2007
-

UF/CISE
-

Newman

12

OSPF Reporting

AS

(domain)

area


Filtering


decides addr import/export


Summarization


addr prefixes, distances

R1

R4

R3

R5

R2

D3

D1

D2

D4

D5

CEN 5501C
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Computer Networks
-

Spring 2007
-

UF/CISE
-

Newman

13

PNNI Hierarchy


Area = Peer Group (hierarchy)


Arbitrary PG interconnection


Hierarchical


Lowest level, node = router


Higher up, node = peer group


Each PG elects “leader”


Leader advertises for PG


PG name is string, prefix = ancestor

CEN 5501C
-

Computer Networks
-

Spring 2007
-

UF/CISE
-

Newman

14

PNNI Connections

Peer Group A

Peer Group B


Higher level connectivity
determined by lower level connections

Peer Group C

AB

AD

ADX

ABX

ADG

BC

CF

CG

CGHF

CGH

CGHV

CEN 5501C
-

Computer Networks
-

Spring 2007
-

UF/CISE
-

Newman

15

PNNI Routing


LSP (unlike NLSP)


Router in a PG knows link state info for all
routers in PG and for all ancestors


Routes at higher levels are PG sequences


Unlike NLSP, can’t restrict use of inter
-
PG
links by limiting information propagation


External link info given without metrics


Could cause loops


Can only flow down, not up (same as IS
-
IS)

CEN 5501C
-

Computer Networks
-

Spring 2007
-

UF/CISE
-

Newman

16

IS
-
IS Area Addresses


variable length


Prefix of CLNP address in CLNP


Area name in IP (level 1 routers don’t talk to
different area level 1 routers)


Area may have multiple addresses (allows
address migration, area merging, splitting)

EX: R1, R3 in A and R2, R4 in B

Add B to R1, R3 and Add A to R2, R4


R1, R2, R3, R4 are in {A,B}

Now delete A from each router’s area addr set

When last router has only B, then all in B

CEN 5501C
-

Computer Networks
-

Spring 2007
-

UF/CISE
-

Newman

17

Area Addresses


OSPF


Single ID, 4 bytes


0.0.0.0 means level 2


NLSP


Similar to IS
-
IS, except IPX prefixes for addrs


Used for default address summary export


PNNI


Variable length string, 0
-
13 bytes long


PG node name = PG name.Leader ID (6 bytes)

CEN 5501C
-

Computer Networks
-

Spring 2007
-

UF/CISE
-

Newman

18

LANs and Designated Routers


DR allows LAN to be treated as a node


N+1 nodes w/N links vs. N nodes w/N
2

links


DR issues link state info for LAN, names LAN


IS
-
IS


determinisitic election


6
-
byte ID and 1
-
byte priority in Hello


Highest (Priority,ID) wins


OSPF


sticky (no preemption of leader)


DR fails, then elect like IS
-
IS


“Better”


less disruptive

CEN 5501C
-

Computer Networks
-

Spring 2007
-

UF/CISE
-

Newman

19

LANs and Designated Routers


NLSP


Similar to IS
-
IS, except


priority += 20 for leader after one min.


Adjust priorities to get IS
-
IS or sticky behavior


PNNI


doesn’t need (pt
-
pt links only)


Peer Group leader elections


Like NLSP, but += 50 after election

CEN 5501C
-

Computer Networks
-

Spring 2007
-

UF/CISE
-

Newman

20

Reliable LSP Propagation on LANs


Easiest way: unicast with ACKs


But high overhead



IS
-
IS


multicast, no ACKs


Assume all went well…


Periodically send Complete Seq # Packet


CSNP gives IDs and seq #’s of LSPs it has


If R sees R’ doesn’t have its latest LSP, resend


If R sees that R’ has more recent LSP for R’’, ask


Request is via Partial Seq # Pkt (like CSNP)


PSNP used to request or to acknowledge

CEN 5501C
-

Computer Networks
-

Spring 2007
-

UF/CISE
-

Newman

21

Reliable LSP Propagation on LANs


OSPF


DR collects explicit ACKs for each LSA (LSP)


DR has lots of state information, backup DR


BDR also listens for LS Advertisement ACKs


R mcasts LSA to AllDRouters (DR and BDR)


DR mcasts the LSA to AllSPFRouters


R’ acks LSA to AllDRouters


If DR lacks enough ACKs, unicast LSA p.r.n.

CEN 5501C
-

Computer Networks
-

Spring 2007
-

UF/CISE
-

Newman

22

Reliable LSP Propagation on LANs


Comparing OSPF and IS
-
IS


OSPF


Extra latency


IS
-
IS


If no updates, constant CSNP overhead


If lots of routing info and many routers, frequent
updates, IS
-
IS has lower overhead (no ACKs)

CEN 5501C
-

Computer Networks
-

Spring 2007
-

UF/CISE
-

Newman

23

Parameter Synchronization


Local Parameters and Global Parameters


Parameters local to link


Can be set using neighbor messages (Hello)


Allow variation across network and even node


E.g. hello frequency, holding time, etc.


Global parameters


Must be uniform over whole network


Can be set using LSPs, or centrally


E.g., field lengths, packet formats, etc.

CEN 5501C
-

Computer Networks
-

Spring 2007
-

UF/CISE
-

Newman

24

IS
-
IS Parameters


Locals


Holding time (officially = 10 x report interval!)


Report interval not exchanged, so OK to vary


Globals


Max # area addresses


Originally 3


ID field size in LSPs


Originally 6 bytes


Later made variable


Value “0” means original value (was rsvd)

CEN 5501C
-

Computer Networks
-

Spring 2007
-

UF/CISE
-

Newman

25

OSPF Parameters


Locals


Hello Interval


RouterDeadInterval


These must match exactly for
all

routers!


CEN 5501C
-

Computer Networks
-

Spring 2007
-

UF/CISE
-

Newman

26

Destinations per Packet


How many destinations can be reported in
an LSP/LSA?


IS
-
IS: Many


Smaller DB (single age for whole)


Must send entire fragment on changes


OSPF: One


Each LSA has own seq#, age => DB is 3x size


Only links that change need to be sent


PNNI: Many


Classes of info, each with own seq #, age

CEN 5501C
-

Computer Networks
-

Spring 2007
-

UF/CISE
-

Newman

27

LSP Database Overload


Static


Underconfigured


Growth


Temporary


E.g., when DR for a LAN changes


Traditional “Solutions”


Crash



Can’t manage remotely if down!


Work with subset


Likely to cause global disruptions

CEN 5501C
-

Computer Networks
-

Spring 2007
-

UF/CISE
-

Newman

28

LSP Database Overloads


IS
-
IS


If LSP doesn’t fit, then don’t ACK


Sender will retry


if temporary, then will fix


Overloaded R will flag itself, other avoid it


Clear flag when no LSP refused for ReTx time


CEN 5501C
-

Computer Networks
-

Spring 2007
-

UF/CISE
-

Newman

29

LSP Database Overloads


OSPF


Overflow more likely (external LSAs)


Traditionally ignored excess LSAs


Disruptive!


Optional capability (RFC 1765)


Deals only with externally generated LSAs


Parameter to set max on such info (and supposed
to be identical but never exchanged…)


Routers should all overflow at same time (
vide supra
)


If overflow, then purge
all

external LSAs!


Leads to “Binge and Purge” behavior

CEN 5501C
-

Computer Networks
-

Spring 2007
-

UF/CISE
-

Newman

30

LSP Database Overloads


PNNI


Designed for ATM, source chooses path


Hence DB overflow less of a problem


Only need to know how to reach neighbors


Restrictions placed on overloaded router


Can’t be PG leader


Can’t be border node


Sets overloaded flag like IS
-
IS


CEN 5501C
-

Computer Networks
-

Spring 2007
-

UF/CISE
-

Newman

31

Authentication


Initially, none in RIP, IS
-
IS


OSPF initial version


had plaintext password as “authentication”


single PW per link


PR caused IS
-
IS to follow suit


Now


Both have cryptographic authentication


OSPF


set by forwarding router (local
-

easier)


IS
-
IS


set by source (more fragile, more secure)


Multiple keys per link


allows migration, more secure

CEN 5501C
-

Computer Networks
-

Spring 2007
-

UF/CISE
-

Newman

32

Interdomain Routing Protocols


Domains


Separate funding, administration, policies


Can select own routing protocol, NW protocol


Interdomain routing protocol


Must be only one! (Why?)


Static Routing


EGP


BGP

CEN 5501C
-

Computer Networks
-

Spring 2007
-

UF/CISE
-

Newman

33

Static Interdomain Routing


Manual configuration of routes


Advantages:


No routing protocol overhead


“Secure” (routers can’t lie to you)


Even routing protocol requires some config


Can handle very complex policies


No possibility of global disruption from faulty
interdomain router in another domain


Disadvantages


No adaptation to changes


Takes a lot of work, may be inconsistent

CEN 5501C
-

Computer Networks
-

Spring 2007
-

UF/CISE
-

Newman

34

EGP


First interdomain routing protocol


Three aspects


Neighbor acquisition


Neighbor reachability


Routing information


Neighbor acquisition


Interior nbor


IG with which EGP info is exchg


Exterior nbor


EG to exchange EGP info with


Nbor acquisition request + reply/refusal


Nbor cease + cease ACK

CEN 5501C
-

Computer Networks
-

Spring 2007
-

UF/CISE
-

Newman

35

EGP


Neighbor reachability


Hello + I heard you


Status: none, you appear reachable, you
appear unreachable (NW info or my NIC)


Seq#


Minimum polling interval (hellos)


Last poll ID number (routing info)


Routing information


DV, but no distance, only reachable!!!!


No loops allowed!

CEN 5501C
-

Computer Networks
-

Spring 2007
-

UF/CISE
-

Newman

36

BGP


Path
-
vector protocol


Given dest and path


Neighbors


E
-
BGP


I
-
BGP


Four message types


Open


acquire nbor


Update


routing info


Notification


link will die


Keepalive
-

hello