Redistribute iBGP Routes into IGP

Issuing redistribute bgp command under IGP routers only redistribute EBGP routes into the IGP. In order to redistribute iBGP learnt routes into IGP redistribute bgp internal command should be used.

To avoid routing loops and IGP routes to preempt iBGP routes, it's recommended to increase the IGP AD to a value higher than iBGP AD (200).

BGP RIB-failure and bgp suppress-inactive

RIB-failure means although the BGP route is valid (reachable next-hop) it's not being installed in the routing table. One of the main reasons for that behaviour is to have an exact match for that route already installed in the routing table with a better administrative distance, which in case of iBGP learnt routes any IGP has better AD.

Such routes with RIB-failure are advertised to BGP peers by default as the hidden command, no bgp suppress-inactive exists under router bgp. If bgp suppress-inactive command those routes will no longer be advertised to BGP peers.

BGP Decision Process and AS_CONFED_SET

Entire AS_CONFED_SET counts as single entry when comparing AS_PATH length.

EBGP Session from Loopback without Increasing TTL

Instead of using neighbor ebgp-multihop, the neighbor disable-connected-check command is used to disable the connection verification process for eBGP peering sessions that are reachable by a single hop but are configured on a loopback interface or otherwise configured with a non-directly connected IP address.

http://www.cisco.com/en/US/docs/ios/12_3t/ip_route/command/reference/ip2_n1gt.html#wp1109875

Enforce Specific Router to Establish BGP Session

Normally the router which has the lowest IP address is responsible to establish the BGP session to remote TCP port 179. However as defined in RFC 4271 (A Border Gateway Protocol 4) - BGP Connection Collision Detection Mechanism - the session originated from the device with higher BGP rouer-id is maintained and the other session is dropped.

To enforce a router to always become the BGP Client (establish TCP session from a high number TCP port to TCP 179), configure loopback addresses in neighbour command and set update-source on the router that you wish to always become client.

Resource Limitation in OSPF

Limit maximum number of LSAs in the database:
R1(config-router)#max-lsa <1-4294967294>

Limit maximum number of redistributed routes:
R1(config-router)#redistribute maximum-prefix <1-4294967294>

To specify the minimum percentage of CPU process time OSPF takes before the CPU should yield to a process with a higher priority:
R1(config-router)#process-min-time percent <1-100>

http://www.cisco.com/en/US/docs/ios/iproute_ospf/command/reference/iro_osp2.html

Sub-second Hello Interval in OSPF

R1(config-if)#ip ospf dead-interval minimal hello-multiplier <3-20>

OSPF Summary and Discard Route

R1(config-router)#area 0 range 100.0.0.0 255.255.192.0
R1(config-router)#no discard-route internal

Same as BGP and EIGRP, when summarising networks in OSPF, it automatically adds a route to Null0 interface. discard-route command stops OSPF from generating that route.

Conditional Default Route with IP SLA in OSPF

R1(config)#ip sla 1

R1(config-ip-sla)#icmp-echo x.x.x.x

R1(config-ip-sla)#frequency y

R1(config-ip-sla)#ip sla schedule 1 life forever start-time now

R1(config)#exit

R1(config)#track 1 ip sla 1

R1(config)# ip prefix-list TRACK_DUMMY permit 1.0.0.1/32

R1(config)#route-map TRACK IPSLA

R1(config-route-map)#match ip add prefix-list TRACK_DUMMY

R1(config)#router ospf 1

R1(config-router)#default-information originate always route-map TRACK_IPSLA

OSPF Type 7 to 5 Translation

• ABR with the highest router-id does the translation (avoid unnecessary and redundant LSA generation)
• Preserves forward address
• There is no type 4 ASBR summary (as forwarding address is preserved)
• Yet the calculation of the final forwarding path stays independent