Now is as good a time to clarify the comparison of Routing Protocols (EIGRP, OSPF and BGP). All routing protocols have their strengths and weaknesses. Thus, to help you select the most appropriate routing protocol for your network. Let's see the comparison routing protocol and the diagram on each routing protocols...
Here is the datasheet/Camparison sheet of Dynamic Routing Protocols for EIGRP, OSPF and BGP (Download: Compare_Table_Routing.xls)
|Administrative Distances||Internal - 90
|110||EBGP - 20
IBGP - 200
|Method||Advanced distance vector||Link state||Path vector|
|Summarization||Auto and manual||Manual||Auto and Manual|
|Convergence Speed||Very fast convergence||Fast||Slow|
|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|
|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
Topology Table LSDB
(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
- 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
- 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
- Keepalive: BGP peers exchange keepalive messages every 60 seconds by default. These keep the peering session
- 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
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 – 0
Redistributed routes metric = IGP metric
The previous diagram illustrates the structure of EIGRP network
The previous diagram illustrates the structure of BGP network