1. Routing Process
   1. Basics
      1. To route packets, Router needs:
         1. Destination Address
         2. Neighbour Routers from which to learn about remote networks
         3. Possible Routes to all remote networks
         4. Best route
         5. How to maintain and verify routing info
   2. MAC addressees
      1. AKA Hardware address
      2. Never leaves LAN
      3. Internal routing
         1. MAC addresses will be of sending host and receiving host
      4. External routing
         1. If heading outside of LAN, MAC addresses will be of sending host and Gateway interface
   3. Frame changed at each hop
      1. Packet unchanged
   4. Frame on a LAN
      1. Takes packet to destination host
      2. Or to Router interface
2. Configuration & Verification
   1. Configuration
      1. Static
         1. from global config mode:
            1. ip route [address] [mask] [next hop address] [AD] [permanent]
            2. Address
            3. Address of the network your routing to
            4. Mask
            5. Subnet mask of the remote network
            6. Next hop
            7. IP address of next router
            8. Can also be exit interface
            9. AD
            10. You can choose the AD of the static route
            11. permanent
            12. The link will stay in the routing table
      2. RIPv1
         1. entered in Global config mode
            1. router rip
            2. network [classful address]
         2. To stop propagation, use passive interfaces
            1. Router (config-router)# passive-interface [interface]
            2. Stops an updates going out configured interface, but can still receive updates
      3. RIPv2
         1. Same as above, just add "version 2" from router config mode
      4. Default routing
         1. should only be used on stub network (network with only one exit)
         2. entered from Global config
            1. ip route 0.0.0.0 0.0.0.0 [next hop/exit interface]
            2. uses wildcard for IP address and mask
            3. tells router to send any IP address not in routing table out of configured network
            4. ip classless
            5. to cover classless addresses being encountered
   2. Verifcation
      1. sh ip route
         1. will show the routing table, and what protocols are being used
      2. sh ip protocols
         1. shows details of which routing protocols are being used
      3. debug ip rip
         1. will show details of RIP updates going in and coming out
3. Routing Protocols
   1. Static Routes
      1. Advantages
         1. No bandwidth, therefore possible cheaper WAN links
         2. No CPU usage
         3. Adds security: Admin can choose who to route to
      2. Disadvantages
         1. Admin needs to understand the network
         2. Any change to network must be entered by hand on each router
         3. Unfeasible in large networks
      3. AD of 1 (by default)
   2. RIPv1
      1. Sends out Entire routing table every 30 seconds
      2. Classful routing only
         1. No VLSM's
         2. All networks have the same Subnet mask
      3. Works well in small networks
         1. Not suitable for large networks, Routing tables too big
      4. maximum hop count of 15
         1. on 16th hop, the packet is dropped
      5. Broadcast based
         1. Sends out updates on 255.255.255.255
      6. No authentication supported
      7. Doesn't support discontiguous networks
      8. Distance Vector Routing Protocol
      9. AD of 120
   3. RIPv2
      1. Same as RIPv1,except
         1. Classless
            1. Supports VLSM's
         2. Multicast based
            1. uses 225.0.0.9
         3. Allows MDS authentication
         4. Supports Discontiguous networks
   4. IGRP
      1. Can be use in large networks
      2. Uses autonomous system number for activation
         1. choose a number and use the same number with each router running IGRP
      3. Updates routing table every 90 seconds
      4. AD of 100
      5. Maximum hop of 255
      6. uses Bandwidth and delay of the line as metric
         1. AKA composite metric
         2. Reliability, load, and MTU can also be used, but not default
      7. Proprietary to Cisco routers
      8. Superseded by EIGRP
4. Routing types
   1. Distance Vector
      1. Judges best path by distance (hops)
         1. Fewer hops = best path
      2. Vector indicates the direction
      3. Send out routing table to neighbours
      4. Susceptible to:
         1. pinhole congestion
            1. where two routes with same AD but different metrics are seen as equal
         2. Slow convergence
            1. time it takes for routing tables to converge
         3. Routing Loops
            1. Where a packet bounces round a network
            2. Fixed with four failsafes:
            3. Maximum hop count
            4. after a total number of hops, packet is dropped
            5. Split Horizon
            6. Routes are not advertised down the same line they were learnt
            7. Route Poisoning
            8. Advertising a route as being unreachable (infinite)
            9. Holddowns
            10. Restricts routers from updating their routes
            11. allows 'flapping' links to stabilise
      5. EG:
         1. RIPv1, RIPv2, IGRP
   2. Link State
      1. Routers create 3 separate tables
         1. 1 for dirrectly attached neighbours
         2. 1 for internetwork topology
         3. 1 for routing
      2. Knows more about internetwork
      3. Send updates on the availability of their own links
      4. EG:
         1. OSPF
   3. Hybrid
      1. Mix of both Distance vector and Link state
      2. EG:
         1. EIGRP