BGPEIGRPGNS3Network TechnologyOSPFProtocols

Comparison of Routing Protocols EIGRP OSPF BGP

Let’s see the comparison routing protocol (EIGRP, OSPF and BGP)

Property EIGRP OSPF  BGP
Administrative Distances Internal – 90

External 170

110 EBGP – 20

IBGP – 200

Method Advanced distance vector Link state Path vector
Summarization Auto and manual Manual Auto and Manual
VLSM Yes Yes Yes
Convergence Speed Very fast convergence Fast Slow
Timers: Update

(hello/dead)

Triggered (LAN 5/15, WAN 60/180) Triggered when network change occurs, send periodic update LSA refreshes every 30 minutes (NBMA 30/120, LAN 10/40) Triggered (60/180)
Network Size Large Large Very large
Mixed-Vendor Devices No Yes Yes
Use multicast  224.0.0.10 224.0.0.5
Feature  – Partial updates conserve network bandwidth

– Support for IP, AppleTalk, and IPX

– Runs directly over IP, using protocol number 88

– Support for all Layer2 (data link layer) protocols and topologies

– Load balancing across equal-and unequal-cost pathways

– Multicast and unicast instead of broadcast address

– Support for authentication

– Manual summarization at any interface

– 100% loop-free classless routing

 – Minimizes the number of routing table entries

– Contains LSA flooding to a reasonable area

– Each routing device takes a copy of the LSA updates its LSDB and forward the LSA to all neighbor devices within area

– Minimizes the impact of a topology change

– Enforces the concept of a hierarchical network design

 – BGP provides the routing betw these autonomouse systems.

– BGP uses the concept of autonomous systems (AS). An autonomous system is a group of networks under a common administration. The Internet Assigned Numbers Authority (IANA) assigns AS numbers: 1 to 64511 are public AS

numbers and 64512 to 65535 are private AS numbers.

– IGP: A routing protocol that exchanges routing infor within AS. RIP, IGRP, OSPF, IS-IS and EIGRP are examples of IFPs.

– EGP: A routing protocol that exchanges routing infor betw different AS. BGP is an example of an EGP.

– The administrative distance for EBGP routes is 20. The administrative distance for IBGP routes is 200.

– BGP neighbors are called peers and must be statically configured.

– BGP uses TCP port 179. BGP peers exchange incremental, triggered route updates and periodic keepalives.

Operation – IP EIGRP Neighbor Table

– IP EIGRP Topology Table AD+FD

– The IP Routing Table

Neighbor Table

Topology Table LSDB

Routing Table

(LSA-> LSDB-> SPF algorithm-> SPF Tree-> Routing Table)

Function is controlled by EIGRP’s function is controlled by 4 key technologies:

– Neighbor discovery and maintenance: Periodic hello messages

– The Reliable Transport Protocol (RTP): Controls sending, tracking, and acknowledging EIGRP messages

– Diffusing Update Algorithm (DUAL): Determines the best loop-free route

– Protocol-independent modules (PDM): Modules are “plug-ins” for IP, IPX, Novel Netware and AppleTalk versions of EIGRP

Following are several types of areas:

– Backbone area: Area 0, which is attached to every other area.

– Regular area: Nonbackbone area; its database contains both internal and external routes.

– Stub area: It’s database contains only internal routes and a default route.

– Totally Stubby Area: Cisco proprietary area designation. Its database contains routes only for its own area and a

default route.

– Not-so-stubby area (NSSA): Its database contains internal routes, routes redistributed from a connected routing

process, and optionally a default route.

– Totally NSSA: Cisco proprietary area designation. Its database contains only routes for its own area, routes redistributed

from a connected routing process, and a default route.

BGP uses 3 databases. The first two listed are BGP-specific; the third is shared by all routing processes on the router:

– Neighbor database: A list of all configured BGP neighbors. To view it, use the show ip bgp summary

command.

– BGP database, or RIB (Routing Information Base): A list of networks known by BGP, along with their

paths and attributes. To view it, use the show ip bgp command.

– Routing table: A list of the paths to each network used by the router, and the next hop for each network. To view

it, use the show ip route command.

Packet Types/BGP Message Types EIGRP uses 5 packet types:

 Hello: Identifies neighbors and serves as a keepalive mechanism sent multicast

 Update: Reliably sends route information unicast to a specific router

 Query: Reliably requests specific route information query packet multicast to its neighbors

 Reply: Reliably responds to a query replies are unicast

 ACK: Acknowledgment

The 5 OSPF packet types follow:

 Hello: Identifies neighbors and serves as a keepalive.

 Link State Request (LSR): Request for a Link State Update (LSU). Contains the type of LSU requested and the

ID of the router requesting it.

 Database Description (DBD): A summary of the LSDB, including the RID and sequence number of each LSA

in the LSDB.

 Link State Update (LSU): Contains a full LSA entry. An LSA includes topology information; for example, the

RID of this router and the RID and cost to each neighbor. One LSU can contain multiple LSAs.

 Link State Acknowledgment (LSAck): Acknowledges all other OSPF packets (except Hellos).

BGP has 4 types of messages:

 Open: After a neighbor is configured, BGP sends an open message to try to establish peering with that neighbor.

Includes information such as autonomous system number, router ID, and hold time.

 Update: Message used to transfer routing information between peers. Includes new routes, withdrawn routes, and

path attributes.

 Keepalive: BGP peers exchange keepalive messages every 60 seconds by default. These keep the peering session

active.

 Notification: When a problem occurs that causes a router to end the BGP peering session, a notification message

is sent to the BGP neighbor and the connection is closed.

Neighbor Discovery and Route Exchange Neighbor Discovery and Route Exchange

Step 1. Router A sends out a hello.

Step 2. Router B sends back a hello and an update. The update contains routing information.

Step 3. Router A acknowledges the update.

Step 4. Router A sends its update.

Step 5. Router B acknowledges.

Establishing Neighbors and Exchanging Routes

Step 1. Down state: OSPF process not yet started, so no Hellos sent.

Step 2. Init state: Router sends Hello packets out all OSPF interfaces.

Step 3. Two-way state: Router receives a Hello from another router that contains its own router ID in the neighbor

list. All other required elements match, so routers can become neighbors.

Step 4. Exstart state: If routers become adjacent (exchange routes), they determine which one starts the

exchange process.

Step 5. Exchange state: Routers exchange DBDs listing the LSAs in their LSD by RID and sequence number.

Step 6. Loading state: Each router compares the DBD received to the contents of its LS database. It then sends a

LSR for missing or outdated LSAs. Each router responds to its neighbor’s LSR with a Link State Update.

Each LSU is acknowledged.

Step 7. Full state: The LSDB has been synchronized with the adjacent neighbor.

BGP Peering States

The command show ip bgp neighbors shows a list of peers and the status of their peering session. This status can

include the following states:

 Idle: No peering; router is looking for neighbor. Idle (admin) means that the neighbor relationship has been

administratively shut down.

 Connect: TCP handshake completed.

 OpenSent, or Active: An open message was sent to try to establish the peering.

 OpenConfirm: Router has received a reply to the open message.

 Established: Routers have a BGP peering session. This is the desired state.

Metric (Calculation) Bandwidth+Delay Cost= 100 Mbps/Bandwidth IBGP  through Attributes

Redistributed routes metric = IGP metric

BGP Attributes list:
Type Code  value Attribute Name Attribute Type
1 ORIGIN Well-known mandatory
2 AS_PATH Well-known mandatory
3 NEXT_HOP Well-known mandatory
4 MULTI_EXIT_DISC (MED) Optional non-transitive
5 LOCAL_PREF Well-known discretionary
6 ATOMIC_AGGREGATE Well-known discretionary
7 AGGREGATOR Optional transitive
8 COMMUNITY Optional transitive
9 ORIGINATOR_ID Optional non-transitive
10 Cluster List Optional non-transitive
11 DPA Designation Point Attribute
12 Advertiser BGP/IDRP Route Server
13 RCID_PATH/CLUSTER_ID BGP/IDRP Route Server
14 Multiprotocol Reachable NLRI Optional non-transitive
15 Multiprotocol Unreachable NLRI Optional non-transitive
16 Extended communities
256 Reserved for future development

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