Routing Protocols

CSCI 690Lecture 5-7

Michael HuttNew York Institute of Technology

Overview Static Routing Dynamic Routing Protocols

Distance Vector Protocols Link State Protocols

Interior Gateway Protocols RIP RIPv2 OSPF IS-IS

Exterior Gateway Protocols BGP4

CIDR - Classless Interdomain Routing Multicast Routing Protocols

Overview…

Route Tableearth#sh ip routeCodes: C - connected, S - static, I - IGRP, R - RIP, M - mobile, B - BGP D - EIGRP, EX - EIGRP external, O - OSPF, IA - OSPF inter area N1 - OSPF NSSA external type 1, N2 - OSPF NSSA external type 2 E1 - OSPF external type 1, E2 - OSPF external type 2, E - EGP i - IS-IS, L1 - IS-IS level-1, L2 - IS-IS level-2, ia - IS-IS inter area * - candidate default, U - per-user static route, o - ODR P - periodic downloaded static route

Gateway of last resort is not set

172.16.0.0/32 is subnetted, 4 subnetsO 172.16.1.4 [110/11] via 192.168.203.253, 00:01:36, Ethernet0C 172.16.1.1 is directly connected, Loopback0O 172.16.1.3 [110/61] via 192.168.203.253, 00:01:37, Ethernet0O 172.16.1.2 [110/1623] via 192.168.203.253, 00:01:37, Ethernet0 192.168.5.0/30 is subnetted, 2 subnetsO 192.168.5.8 [110/60] via 192.168.203.253, 00:01:37, Ethernet0O 192.168.5.0 [110/1622] via 192.168.203.253, 00:01:37, Ethernet0 10.0.0.0/32 is subnetted, 1 subnetsO 10.1.1.1 [110/1623] via 192.168.203.253, 00:01:37, Ethernet0C 192.168.203.0/24 is directly connected, Ethernet0C 192.168.1.0/24 is directly connected, Ethernet1O 192.168.103.0/24 [110/1632] via 192.168.203.253, 00:01:37, Ethernet0

Static Routesearth#sh ip routeCodes: C - connected, S - static, I - IGRP, R - RIP, M - mobile, B - BGP D - EIGRP, EX - EIGRP external, O - OSPF, IA - OSPF inter area N1 - OSPF NSSA external type 1, N2 - OSPF NSSA external type 2 E1 - OSPF external type 1, E2 - OSPF external type 2, E - EGP i - IS-IS, L1 - IS-IS level-1, L2 - IS-IS level-2, ia - IS-IS inter

area * - candidate default, U - per-user static route, o - ODR P - periodic downloaded static route

Gateway of last resort is 192.168.1.1 to network 0.0.0.0

172.17.0.0/24 is subnetted, 1 subnetsS 172.17.1.0 is directly connected, Ethernet1

Dynamic Routing Protocols Dynamically create and update routing tables Compensate for topology changes IP Routing Protocols

RIP RIPv2 IGRP (Cisco Only) EIGRP (Cisco Only) OSPF IS-IS BGP4 EGP

Routers must be using the same protocol to shareinformation

Routing Protocol Basics Path Determination

Install directly connected networks in the routing tablebased on interface configuration

interface Ethernet1 description backbone connection ip address 192.168.1.254 255.255.255.0 ip pim sparse-dense-mode

earth#sh ip route 192.168.1.0Routing entry for 192.168.1.0/24 Known via "connected", distance 0, metric 0

(connected, via interface) Routing Descriptor Blocks: * directly connected, via Ethernet1 Route metric is 0, traffic share count is 1

Routing Protocol Basics… Metrics - to choose from multiple routes to the same

destination

Hop Count Counts router hops

Bandwidth Load

Traffic utilization Delay Reliability

Errors on link Cost

Configured by network admin

Routing Protocol Basics…earth#sh int e1Ethernet1 is up, line protocol is up Hardware is Lance, address is 00e0.b064.0b7d (bia 00e0.b064.0b7d) Description: backbone connection Internet address is 192.168.1.254/24 MTU 1500 bytes, BW 10000 Kbit, DLY 1000 usec, reliability 255/255, txload 1/255, rxload 1/255 Encapsulation ARPA, loopback not set Keepalive set (10 sec) ARP type: ARPA, ARP Timeout 04:00:00 Last input 00:00:00, output 00:00:00, output hang never Last clearing of "show interface" counters never Input queue: 1/75/0/0 (size/max/drops/flushes); Total output drops: 0 Queueing strategy: fifo Output queue :0/40 (size/max) 5 minute input rate 0 bits/sec, 0 packets/sec 5 minute output rate 0 bits/sec, 0 packets/sec 2099 packets input, 163455 bytes, 0 no buffer Received 269 broadcasts, 0 runts, 0 giants, 0 throttles 0 input errors, 0 CRC, 0 frame, 0 overrun, 0 ignored 0 input packets with dribble condition detected 2005 packets output, 160113 bytes, 0 underruns 0 output errors, 0 collisions, 21 interface resets 0 babbles, 0 late collision, 0 deferred 0 lost carrier, 0 no carrier 0 output buffer failures, 0 output buffers swapped out

Routing Protocol Basics…

Convergence The process of bringing all route tables to a state

of consistency

Load Balancing Optionally alternate traffic between multiple paths Packet by packet or session by session

(destination)

Distance Vector Protocols

R.E. Bellman, L.R. Ford and D.R. Fulkerson

Bellman-Ford or Ford-Fulkerson Algorithms

Advertise routes as a vector containing (distance,direction) destination 192.168.103.0/24 is 3 hops away in

the direction of 192.168.203.253

Distance Vector Protocols…

Routers will periodically send updates to theirneighbors by broadcasting their entire routingtable

RIP for example broadcasts its routing tableto its neighbors every 30 sec

After 3 to 6 update periods if info about acertain route is not included it is removedfrom the routing table

Distance Vector Protocols… Split Horizon

Routes are not advertised back out the interfacethey were received from

Prevents routing loops by not advertising reverseroutes

Split Horizon with poisoned reverse Advertises reverse routes but with a metric (hop

count) of infinity

Distance Vector Protocols…

Counting to Infinity Define infinity to be 16 Hop count of 16 means network is

unreachable

Distance Vector Protocols…

Triggered Updates as soon as a metric changes an update is

immediately sent

Hold-down Timers if a metric changes for a route, don’t accept any

new updates until the timer expires - reducelikelihood of bad routing info as changes in thenetwork are occurring

Link State Protocols Each router has a complete picture of the network

and can compute its own best paths

The topology information in each router is identical

Shortest path first or distributed database protocols

Dijkstra’s Algorithm

OSPF and IS-IS

Link State Protocols… An adjacency is established with each neighbor Each router sends LSAs (link state advertisements)

to each neighbor LSA contains link identifier, state of the link, metric

cost of the link, and any neighbors connected viathat link

Each neighbor floods all LSAa received to all itsneighbors

Once the topology or link state database is completeeach router can compute the shortest path to anydestination using Dijkstra’s algorithm and update itsown routing table

Link State Protocols…

Routers send hello packets containing arouter ID (ip address of an interface - e.g.,Loopback0) to establish adjacencies with itsneighbors

If hello packets are not heard e.g., every 10s,then the adjacency is broken after say 4timeouts, and the neighbor is consideredunreachable

Link State Protocols…

LSAs are flooded immediately when achange occurs

Convergence is much quicker than withdistance vector protocols

Sequence numbers are used to detectduplicate LSAs

Link State Protocols… Sequence number spaces can be linear or circular

IS-IS uses a 32 bit linear sequence number space

Finding the larger number in a circular sequencenumber space a > b and (a-b) <= n/2 a < b and (b-a) > n/2

if n = 6 and we’re given 48 and 18 48 > 18 and (48-18) = 30 and 30 < 32, so 48 is more recent

Link State Protocols… Lollipop-Shaped Sequence Number Spaces

Hybrid of linear and circular number spaces Linear number space forms the stick - used for

restarts Circular number space forms lollipop - after a

router restarts and receives an LSA from aneighbor it can jump back to the circular portion -where it was before it restarted

Link State Protocols…

Each LSA contains an age field initialized tozero

Each router increments the field when theLSA is received

If two LSAs with the same sequence numberand different ages are received, the age canbe used to determine which one to keep(routing protocol specific based onMaxAgeDiff)

Link State Protocols…earth#sh ip ospf database

OSPF Router with ID (172.16.1.1) (Process ID 100)

Router Link States (Area 0)

Link ID ADV Router Age Seq# Checksum Link count172.16.1.1 172.16.1.1 1134 0x80000007 0x7D6D 3172.16.1.2 172.16.1.2 1034 0x80000007 0x2DBC 5172.16.1.3 172.16.1.3 1058 0x80000009 0x8B33 5172.16.1.4 172.16.1.4 1093 0x80000009 0x62D3 4

Net Link States (Area 0)

Link ID ADV Router Age Seq# Checksum192.168.203.253 172.16.1.4 1093 0x80000006 0x3689

Link State Protocols…

Link State Database

Router link information (routerID, neighborID,cost)

Stub network information (routerID, networkID,cost) - network with no neighbors

Dijkstra’s algorithm is run by each router in thenetwork to build its own routing table

Link State Protocols…

Area - subset of routers that make up aninternetwork

Area Border Routers (ABRs) connect areas ABRs pass a summary of the link state info

Dijkstra’s Algorithm

C 0 CF 2 C -> FB 2 C -> BG 3 C -> F -> GE 3 C -> B -> ED 5 C -> B -> E -> DA 7 C -> B -> E -> D -> A

Dijkstra’s Algorithm…7 nodes in the network: F A D C G E Bunsolved C D A F B E Gworking on C...checking neighbor F...new dist for F: 2, prev: Cchecking neighbor G...new dist for G: 5, prev: Cchecking neighbor B...new dist for B: 2, prev: Cunsolved F B G E A Dworking on F...checking neighbor C...old dist for C: 0, prev: Cchecking neighbor G...new dist for G: 3, prev: Fchecking neighbor E...new dist for E: 6, prev: Funsolved B G E A Dworking on B...checking neighbor A...new dist for A: 8, prev: Bchecking neighbor C...old dist for C: 0, prev: Cchecking neighbor E...new dist for E: 3, prev: Bunsolved G E A Dworking on G...checking neighbor F...old dist for F: 2, prev: Cchecking neighbor C...old dist for C: 0, prev: Cunsolved E A Dworking on E...checking neighbor F...old dist for F: 2, prev: Cchecking neighbor D...new dist for D: 5, prev: Echecking neighbor B...old dist for B: 2, prev: Cunsolved D Aworking on D...checking neighbor A...new dist for A: 7, prev: Dchecking neighbor E...old dist for E: 3, prev: Bunsolved Aworking on A...checking neighbor D...old dist for D: 5, prev: Echecking neighbor B...old dist for B: 2, prev: C

Autonomous System (AS) An internetwork under a common administration Interior Gateway Protocols run within an AS Distance Vector and Link State protocols are IGPs Exterior Gateway Protocols route between

Autonomous Systems BGP4 EGP IDRP (ISO’s InterDomain Routing Protocol)

IGP vs EGP

RIP Routing Information Protocol Classful routing protocol Uses UDP port 520 Updates are broadcast out all RIP enabled

interfaces every 30 seconds If an update for a route is not heard in 180 seconds

the route is set as unreachable (hop count of 16) Workstations can run RIP (routed) routed -q - listens to RIP but does not generate RIP

updates Broadcasts contain up to 25 routes at a time

RIP… Classful routing RIP does not advertise a subnet mask in its updates The router must use the mask configured on one of

its interfaces and assume that is the mask usedthroughout the network

jupiter# debug ip rip*Mar 1 04:48:20.113 UTC: RIP: sending v1 update to 255.255.255.255 via Ethernet0/0

(192.168.203.253)*Mar 1 04:48:20.113 UTC: RIP: build update entries - suppressing null update*Mar 1 04:48:20.702 UTC: RIP: received v1 update from 192.168.203.254 on Ethernet0/0*Mar 1 04:48:20.706 UTC: 192.168.1.0 in 1 hops

R 192.168.1.0/24 [120/1] via 192.168.203.254, 00:00:02, Ethernet0/0

RIP Version 2

Authentication (MD5) Route Tag for interaction with EGPs (BGP) Routing updates now contain subnet mask

info - supports VLSM Next to which packets should be forwarded,

e.g., skip hops where RIP is not being run Multicast route updates to 224.0.0.9

RIPv2 VLSM

Variable Length Subnet MaskingBreak up an address using different subnet masks

Subnet/Mask Address Range Broadcast Address

192.168.50.0/25 192.168.50.1 - 192.168.50.126 192.168.50.127

192.168.50.128/26 192.168.50.129 - 192.168.50.190 192.168.50.191

192.168.50.192/27 192.168.50.193 - 192.168.50.222 192.168.50.223

192.168.50.224/28 192.168.50.225 - 192.168.50.238 192.168.50.239

192.168.50.240/30 192.168.50.241 - 192.168.50.242 192.168.50.243

192.168.50.244/30 192.168.50.245 - 192.168.50.246 192.168.50.247

OSPF IETF Recommended IGP

Link State Protocol

Uses Dijkstra’s SPF Algorithm

V1 only experimental

V2 used in production environments

OSPF… Use of areas reduces load on cpu

Fully classless - supports VLSM

Uses multicast to flood LSAs

Supports authentication

Operation of OSPF Send hello packets to find neighbors Form adjacencies between neighbors Send LSAs over all adjacencies Each router records each LSA in its Link State

Database By flooding LSAs all routers build identical

databases When DBs are complete each router runs SPF

algorithm to find shortest path to each destination Each router builds its own routing table from the

shortest path trees

Neighbors and Adjacencies Router ID - numerically highest IP address on any

of the loopback interfaces (Cisco) Router ID is advertised to neighbors in hello packets Hello protocol used to discover neighbors Hello protocol acts as keepalives between neighbors Hello protocol elects Designated Routers (DRs) and

Backup DRs on broadcast networks

Designated Routers Multiaccess networks with n routers will form n*(n-

1)/2 adjacencies For example 5 routers connected to an ethernet will

form 10 adjacencies (fully meshed) Each router would flood 4 LSAs plus one LSA for

the common ethernet Only the DR floods LSAs to the internetwork A backup DR is also elected All routers form adjacencies with the DR and BDR

OSFP Interfaceearth#sh ip ospf intEthernet0 is up, line protocol is up Internet Address 192.168.203.254/24, Area 0 Process ID 100, Router ID 172.16.1.1, Network Type BROADCAST, Cost: 10 Transmit Delay is 1 sec, State BDR, Priority 1 Designated Router (ID) 172.16.1.4, Interface address 192.168.203.253 Backup Designated router (ID) 172.16.1.1, Interface address

192.168.203.254 Timer intervals configured, Hello 10, Dead 40, Wait 40, Retransmit 5 Hello due in 00:00:09 Index 3/3, flood queue length 0 Next 0x0(0)/0x0(0) Last flood scan length is 1, maximum is 1 Last flood scan time is 0 msec, maximum is 0 msec Neighbor Count is 1, Adjacent neighbor count is 1 Adjacent with neighbor 172.16.1.4 (Designated Router) Suppress hello for 0 neighbor(s)

OSPF Areas Reduces size of link state database Reduces load on cpu Reduces flooding - limited to the area Uses 32 bit area ID Area 0 is reserved for the backbone Backbone summarized topographies of each

area to every other area Every area must connect to area 0 via an

area border router (ABR)

OSPF Areas…

Types of Traffic

Intra-area - traffic within a single area

Inter-area - traffic between areas

External - traffic from another AS

OSPF Areas… Router Types

Internal Routers - routers have a single link statedatabase. All interfaces are in the same area

Area Border Router - connects one or more areasto the backbone. Maintains separate link statedatabases for each area

Backbone Routers - all interfaces belong to area 0 Autonomous System Boundary Router (ASBR) -

gateways for external traffic

OSPF Areas… Partitioned Area

Isolated Area

Virtual Links A link to the backbone through a non-backbone area

Used to connect two parts of a partitioned backbonethrough a non-backbone area

Must be configured between ABRs

Partitioned Area

Partitioned Backbone

Virtual Link

OSPF Link State Database Stores all LSAs LSAs are flushed are 60 min, so updates are sent

every 30 min 11 Different types of LSAs

Router LSA - lists all router links along with state and cost Network LSA - sent by DR, lists all attached routers Opaque LSAs - advertise application specific info. E.g.,

bandwidth usage for traffic engineering External LSAs - flooded by ASBRs

OSFP Stub Area

Area into which AS External LSAs are NOTflooded

All traffic must pass through the ABR toreach the external networks

ABR uses Network Summary LSAs toadvertise a single default route

Not-So-Stubby-Areas Allow external routes to be advertised into OSPF

NSSA

IS-IS Intermediate System to Intermediate System

Routing protocol for ISO’s ConnectionlessNetwork Protocol (CLNP)

Integrated IS-IS or Dual IS-IS Extension to IS-IS to support transition from

TCP/IP to OSI Could route both IP and CLNS

IS-IS Areas

Area borders are on links not routers Routers connecting areas are level 2 routers Routers with no direct connection to another

area are level 1 routers Routers can be L1, L2 or L1/L2 L2 and L1/L2 router form the IS-IS backbone Distributes link state info in Link State PDUs,

not LSAs

Network Entity Title

IS-IS Router Address area id.system id.sel 07.0000.3090.c7df.00 If sel is something other than zero, than it is a

Network Service Access Point (NSAP) System id will usually be set to a mac

address to ensure it’s unique

Border Gateway Protocol 4(BGP4) Exterior Routing and Autonomous Systems Basic Messages CIDR Path Vector Protocol Path Attributes

http://www.bgp4.as/

BGP4

An Exterior Gateway Protocol (EGP), used topropagate tens or hundreds of thousands ofroutes between networks (ASs).

The only protocol used to do this on theInternet today.

BGP4 Overview The Border Gateway Protocol, currently Version 4 -

defined in RFC 1771, and extended (with additionaloptional attributes) in other RFCs.

A “path-vector” routing protocol, running over TCPport 179.

Supports modern “classless” routing. BGP3, RIPv1,and some others do NOT.

Version 4 handles aggregation (CIDR) andsupernetting

BGP4 and AS Numbers

AS 4969

AS 5000

AS 6461

AS 701

AS 12001

Basic Messages Open

Initiates BGP session between routers Update

Advertise routing information Notification

Used to report an error KeepAlive Route-Refresh

Specific request for a router to re-advertise all its routes

Basic Messages…

BGP Speaker - can send and receive BGPmessages

BGP Peers - pair of routers that exchangeBGP messages

Classless Interdomain Routing(CIDR)

Reduces the size of routing tables Uses prefix notation 192.32.0.0/16 - illegal class C network With CIDR 192.32.0.0/16 is a supernet

Prefix contains fewer bits than the natural mask 192.32.1.0/20 - more specific Longer mask always used for routing

Longest Match Routing Rule

CIDR Example

192.24.160.0/19

Netmask: 255.255.224.0

Wild card mask: 0.0.31.255

CIDR Address Range 192.24.160.0 - 192.24.191.255

CIDR Conversion TableCIDR Length Mask # Networks /1 128.0.0.0 128 A /2 192.0.0.0 64 A /3 224.0.0.0 32 A /4 240.0.0.0 16 A /5 248.0.0.0 8 A /6 252.0.0.0 4 A /7 254.0.0.0 2 A /8 255.0.0.0 1 A or 256 B /9 255.128.0.0 128 B /10 255.192.0.0 64 B /11 255.224.0.0 32 B /12 255.240.0.0 16 B /13 255.248.0.0 8 B /14 255.252.0.0 4 B /15 255.254.0.0 2 B /16 255.255.0.0 1 B or 256 C /17 255.255.128.0 128 C /18 255.255.192.0 64 C /19 255.255.224.0 32 C /20 255.255.240.0 16 C /21 255.255.248.0 8 C /22 255.255.252.0 4 C /23 255.255.254.0 2 C /24 255.255.255.0 1 C /25 255.255.255.128 1/2 C /26 255.255.255.192 1/4 C /27 255.255.255.224 1/8 C /28 255.255.255.240 1/16 C /29 255.255.255.248 1/32 C /30 255.255.255.252 1/64 C /31 255.255.255.254 1/128 C /32 255.255.255.255 1/256 C

Path Vector Protocol

Sequence of AS numbers to indicate the patha route has traversed

Network Layer ReachabilityInformation(NLRI) <length, prefix> Lists destinations <19,192.24.160.0> 192.24.160.0/19

Path Attributes ORIGIN (type code 1) AS_path (type code 2) NEXT_HOP (type code 3) MULTI_EXIT_DISC (type code 4) LOCAL_PREF (type code 5) ATOMIC_AGGREGATE (type code 6) AGGREGATOR (type code 7) COMMUNITY (type code 8) ORIGINATOR_ID (type code 9) Cluster List (type code 10)

AS Path

AS numbers are prepended to the path

AS Path Manipulation

Can repeat AS number to make path look worse

The Local Preference Attribute Higher local pref indicates a route is more preferred

for a specific destination Used to select links for OUTGOING traffic

The MULTI_EXIT_DISC (MED)Attribute

Hint to external neighbors about the preferredpath into an AS

Lower MED value is preferred over a highervalue

MED is exchanged between ASs

The Community Attribute A group of destinations that share some

common property

Not restricted to a single AS

Example: educational or governmentcommunity

Simplify routing policies

Other Routing Protocols

IGRP EIGRP ES-IS - ISO protocol to run between end

systems and routers Interdomain Routing Protocol (IDRP) - ISO

standard built on BGP Hot Standby Router Protocol (HSRP)

HSRP

Cisco Protocol (Patented) Represents multiple routers as a virtual

router Routers share a virtual IP and MAC address Virtual Router Redundancy Protocol (VRRP)

- open protocol freely available

HSRP…

jupiter#sh standbyEthernet0/0 - Group 0 Local state is Standby, priority 100 Hellotime 3 sec, holdtime 10 sec Next hello sent in 1.922 Virtual IP address is 192.168.203.1 configured Active router is 192.168.203.254, priority 105 expires in 7.360 Standby router is local 1 state changes, last state change 00:05:31 IP redundancy name is "hsrp-Et0/0-0" (default)

HSRP…earth#sh standbyEthernet0 - Group 0 Local state is Active, priority 105, may preempt Hellotime 3 sec, holdtime 10 sec Next hello sent in 1.330 Virtual IP address is 192.168.203.1 configured Active router is local Standby router is 192.168.203.253 expires in 8.932 Virtual mac address is 0000.0c07.ac00 2 state changes, last state change 00:11:21

Multicast Routing Protocols

Multicast Basics Distribution Trees Reverse Path Forwarding TTL Check Protocol Categories IGMP PIM-SM

Multicast Basics Multicast uses class D addresses (groups) Hosts must join the group they wish to receive traffic

on Link Local Multicast Addresses

IANA reserved 224.0.0.0 through 224.0.0.255 for use bynetwork protocols on a local segment

E.g. 224.0.0.2 All Multicast Routers 224.0.0.5 OSPF Routers 224.0.0.13 All PIM Routers

Multicast Basics…

Administratively Scoped Multicast Addresses IANA reserves 239.0.0.0 through

239.255.255.255 for use in private multicastdomains

Ethernet Multicast MAC Address Mapping 01:00:5e:xx:xx:xx only low order 23 bits are available to map IP

address 32 to 1 overlap

Multicast Distribution Trees Source Trees

Tree rooted at source Branches form a spanning tree through the network Uses the shortest path through the network Also called SPT - shortest path tree SPT is enumerated by the Source and Group (S,G) A separate SPT exists for each (S,G)

Shared Trees Uses a single common root Rendezvous Point (RP) or Core RP trees or Core based trees All sources send traffic to the root Tree represented by (*,G)

Source Trees

Shared Tree

Reverse Path Forwarding

Router checks source IP address of packet todetermine if the packet arrived via aninterface that is on the reverse path back tothe source.

If the packet arrives on the interface leadingback to the source the RPF check issuccessful and the packet is forwarded.

If the RPF check fails, the packet isdiscarded.

RPF Check

Router needs to consult routing table to findreverse path back to the source

If RPF check is successful, the packet isforwarded to all interfaces in the OIL.

s0e0s1

192.168.1.0/24172.16.0.0/16151.10.0.0/16

InterfaceNetwork

RPF Check…

Which routing table to use: DVMRP maintains a separate routing table and

uses this for the RPF check PIM and CBT use the unicast routing table

Distance Vector Multicast Routing Protocol(DVMRP)

Protocol Independent Multicast (PIM) Core-Based Trees (CBT)

TTL Thresholds

TTL Scoping A router’s interface can be configured to only

forward multicast packets if the ttl is greater thana certain value.

TTL = 0 stays within the source host

TTL = 1, stays on local subnet

Multicast Routing ProtocolCategories

Dense Mode Protocols DVMRP PIM-DM

Sparse Mode Protocols PIM-SM CBT

Link State Protocols MOSPF

Dense Mode Protocols Employ only SPTs to delivery (S,G) multicast traffic

using the push principle Assume every subnet in the network wants to

receive the multicast Floods multicast to all points in the network Prune back tree where there are no multicast

receivers When a prune message is received, the interface

that the message was received on is removed fromthe oil

Sparse Mode Protocols Make use of shared trees, and occasionally SPTs Uses pull model - receivers must issue an explicit

JOIN Shared tree branch must be constructed from the

root Routers forward the shared JOIN towards the RP PIM-SM also allows SPT joins toward the source to

build an SPT Prune messages are sent when hosts leave the tree

Link State Protocols

MOSPF uses SPTs to distribute multicasttraffic

Flood/Prune mechanism is not used Flood special multicast, link state info that

identifies the location of receivers. Each router then builds SPTs from each

source to the receivers in the group.

IGMP V1

Membership Query Membership Report

V2 Membership Query

General Query Group-Specific Query

V1 Membership Report V2 Membership Report Leave Group

IGMPv3From RFC 3376

Version 3 adds support for "source filtering", that is, the ability for asystem to report interest in receiving packets *only* from specificsource addresses, as required to support Source-Specific Multicast[SSM], or from *all but* specific source addresses, sent to a particularmulticast address. Version 3 is designed to be interoperable withVersions 1 and 2.

PIM-SM Protocol Independent

uses unicast routing table for RPF check Explicit Join Model Shared Trees Shortest Path Trees (SPT) Source Registration Designated Router (DR) STP Switchover RP Discovery

Shared Trees

Receiver sends IGMP Report for Group GRouter C places the interface in its OILSends PIM join towards RP - join shared tree

Shortest Path Trees

Source Registration

PIM uses unidirectional trees Traffic can only flow down the tree from the

RP RP joins the SPT back to the source to get

traffic to the RP PIM Register message sent by first hop DR

to RP to notify RP that Source S is sending toGroup G

Designated Router

DR sends PIM join messages towards theRP when more than one router exists on asubnet

PIM Hello messages can also detect thefailure of the DR

SPT Switchover SPT threshold (bandwidth)

If the threshold is exceeded the last-hop DR joinsthe SPT

If the threshold is zero then the SPT is joined assoon as the first multicast packet is received via theshared tree

If SPT threshold is infinity, the SPT is never joined

RP Discovery

Static configuration - ok for small networks

PIMv2 bootstrap mechanism allows all PIM-SM routers to lean all group-to-RP mappingsand avoid manual RP configuration

Cisco Auto-RP was developed prior to PIMv2