Dynamic Routing Protocols #
| Protocol | Type | IGP or BGP? | Notes |
|---|---|---|---|
| RIPv1 | Distance vector | IGP | Old; only used variable subnets within an AS |
| RIPv2 | Distance vector | IGP | Supports VLSM and discontiguous subnets |
| BGP | Path vector | BGP | Used on the Internet, connects AS' |
| OSPF | Link State | IGP | Fast, popular, uses ARea IDs (Area 0/backbone) |
| IS-IS | Link state | IGP | Alternative to OSPF |
| EIGRP | Hybrid | IGP | Cisco proprietary |
Distance Vector #
Compares cost of all routes to a particular network ID and chooses the lowest cost.
RIPv1 #
See also: Routing Information Protocol (RIP)
Maximum hop count of 15. Sends routing tables every 30 seconds. Doesn’t know how to use variable-length subnet masking (VLSM). Open to attack, no authentication.
RIPv2 #
Same as RIPv1 except VLSM and authentication has been added. Only suitable for small private networks. Time to convergence still too long for WANs.
Path Vector #
BGP #
Border Gateway Protocol (BGP) Current version is BGP-4
- Multitiered structure and at the top sit many Autonomous Systems (AS).
- Each AS is governed by a single dynamic routing protocol.
- AS' deliver data to each other using an Autonomous System Number (ASN) assigned by the IANA.
- ASNs are 32 bit numbers displayed as 2 16-bit numbers separated by a dot. 1.33457
EGP #
communicate with each other using a protocol called the Exterior Gateway Protocol (EGP). e internet has settled on BGP as the EGP.
Interior gateway protocol (IGP) #
tworsk with an AS communicate with each other using Interior Gateway Protocols (IGPs).
Link State #
See also:
Open Shortest Path First (OSPF) #
- Most commonly used IGP in the world
- Converges faster and much more efficient than RIP
- Two adjacent routers form a neighborship through Hello packets
- Exchange information about routers through link state advertisement (LSA) packets.
- OSPF’s metric is cost, which is a function of bandwidth. Chooses lowest cost.
- Shortest path first, by definition, prevents loops.
IS-IS #
Intermediate System to Intermediate System Very similar to OSPF, but added advantage that IPv6 was baked in from the start. This is the de afcto standard for ISPs.
EIGRP #
Enhanced Interior Gateway Routing Protocol
- Shares aspects of both distance vector and link state protocols.
- Invented by Cisco
- Called an advanced distance vector protocol.