Types of dynamic routing protocols:
RIP : Routing Information Protocol - AD 120 IGRP : Interior Gateway Routing Protocol - AD-100 EIGRP : Enhanced IGRP AD-90 OSPF : Open Shortest Path First AD-110 IS-IS : Intermediate system to intermediate system AD-115 BGP: Border Gateway Protocol AD-20
Comparison
| 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 – 0 Redistributed routes metric = IGP metric |
Reference:
http://cisconetworkingcenter.blogspot.com/2013/01/comparison-of-routing-protocols-eigrp.html
