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>

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

BGP Backdoor

Can be used to favour IGP routes instead of eBGP routes when both exist in the routing table as the default AD for eBGP route is lower than any IGP route.

network <network address> backdoor

The specified network address is treated as a local entry, but not advertised as a normal network entry.

http://www.cisco.com/en/US/tech/tk365/technologies_tech_note09186a00800c95bb.shtml#bgpbackdoor

IPv6 Redistribute with include-connected

For IPv6 whether or not connected links are included in redistribution is up to you at the time of configuration.


http://blog.ine.com/2008/01/15/understanding-how-redistribution-works-in-ipv6/

Differences between OSPFv3 and OSPFv2

1. Configured using interface command
2. Advertising multiple networks on an interface
3. OSPFv3 RID must be set
4. Flooding scope (link-local, area, AS)
5. Multiple instance per link
6. Source packets from link-local address (except virtual link)
7. Authentication using AH / ESP
8. New LSA Types:

1. Intra-Area Prefix LSA (Type 9)
2. Link LSA (Type 8)
1. Router LSA can be split across multiple LSAs; Link State ID in LSA header is a fragment ID

http://academy.itu.int/moodle/pluginfile.php/38185/mod_resource/content/1/4%20-%20OSPFv3.pdf

Differences between EIGRP for IPv4 and IPv6

1. Configured on interface
2. Must no shut the routing process
3. 32-bit router ID
4. Passive interface
5. Route filtering: only distribute-list prefix-list
6. Automatic summarisation
7. Cisco IOS support: 12.4(6)T
8. No auto-summary, as there is no classful concept anymore

CCIE Routing and Switching Certification Guide (4th edition)

IPv6 Neighbour Discovery Lifetime

The value indicates the usefulness of the router as a default router on this interface.Setting the value to 0 indicates that the router should not be considered a default router on this interface.

ipv6 nd ra lifetime superseded the old ipv6 nd ra-lifetime interface command.

EIGRP Interface Load (K2)

EIGRP routing updates are triggered only by a change in network topology (interface up/down event, IP addressing change or configured bandwidth/delay change) and not by change in interface load or reliability. The load/reliability numbers are thus a snapshot taken at the moment of the topology change and should be ignored.

http://blog.ioshints.info/2009/06/eigrp-load-and-reliability-metrics.html

EIGRP routing over DMVPN (mGRE)

On Hub:

• Disable as-member split-horizon
• Disable as-member next-hop-self

EIGRP traffic-share min

when you use the traffic-share command with the keyword min, the traffic is sent only across the minimum-cost path, even when there are multiple paths in the routing table. This is identical to the forwarding behaviour without use of the variance command. However, if you use the traffic-share min command and the variance command, even though traffic is sent over the minimum-cost path only, all feasible routes get installed into the routing table, which decreases convergence times.

1. traffic-share balanced (default):
1. Variance=1 (default):
1. Traffic will be sent to successor(s) only (equal cost load balancing).
2. Feasible successors are kept in EIGRP topology table.
3. Feasible successors are not kept in the routing table.
2. Variance=2+:
1. Traffic will be sent to successor(s) and feasible successors(s).
2. Traffic will be sent inversely proportional to their metrics.
3. All successor(s) and feasible successor(s) are kept in the routing table.
2. traffic-share min across-interfaces:
1. Variance=1 (default):
1. same as (1.1)
2. Variance=2+:
1. Traffic will be sent to successor(s) only (equal cost load balancing).
2. Feasible successors are kept in the routing table.

http://www.cisco.com/en/US/tech/tk365/technologies_tech_note09186a008009437d.shtml

http://blog.ine.com/2009/05/01/understanding-unequal-cost-load-balancing/

OSPF Default Route Cost

set on ABR:
area [area-number] default-cost [cost]

OSPF Forwarding Address and How to Suppress It

If the forwarding address in an external LSA is specified, and this address is not reachable, the address contained in the LSA is not inserted into the route table. When NSSA ABR translates the type 7 NSSA LSA into they 5 LSA, by default the forwarding address is transferred from type 7 to type 5. The ABR can be configured to suppress the forwarding address during the translation, replacing the specified address with the address 0.0.0.0. When another router receives the type 5 external LSA with the forwarding address suppressed, instead of trying to direct traffic for the external address to the forwarding address the receiving router will attempt to direct the traffic to the toe 7 to type 5 translating ABR router.

area 10 nssa translate type 7 suppress-fa

Routing TCP/IP Volume 2, Second Edition

area range Command

area range command specifies the area to which the summary adress belongs, the summary address, and the address mask.

It also installs a route to the null interface automatically. The router can be configured to not install it in the route table using the command no discard-route.

no-advertise switch is used for filtering summary addresses to be advertise to backbone network.

Routing TCP/IP Volume 2, Second Edition