EIGRP Redistribution

EIGRP redistribution

There is no default metric for EIGRP so you need to manually configure metric when you redistribute routes from other routing protocol. But there are some exceptions:

1. Static route using next hop
          EIGRP will redistribute the static route using the exiting (next hop) interface's metric

2. IGRP
          If they have the same AS number, it will automatically redistribute between each other. Otherwise you need to manually configure but not need to configure metric.

3. Static route using interface
          You can use network statement (EIGRP internal route) or redistribute static (EIGRP external route) to advertise the route.

Route-map for Redistribution

1. match ip next-hop prefix-list is not supported in redistribution route-map.
So it is better to use ACL whenever is possible in route-map when doing redistribution.

BGP OSPF redistribution.

1. By default, BGP only redistribute ospf network type internal. To redistribute other type of ospf network, you need to add to the redistribution
redistribute ospf 1 ------ Only internal (intra and inter-area) routes
redistribute ospf 1 match external ---- Only external type 1 and 2 route
redistribute ospf 1 match internal external 2 --- only internal and external type 2
redistribute ospf 1 match nssa-external 1 ---- Only nssa-external type 1.

2. By default, iBGP redistribution into IGP is disabled.
Issue the bgp redistribute-internal command under router bgp process in order to enable redistribution of iBGP routes into IGP.

3. BGP and OSPF router-id
If BGP synchronization is enabled, there must be a match for the prefix in the IP routing table in order for an internal BGP (iBGP) path to be considered a valid path.

4. Link for tips. 911network.

Timer for different routing protocol

1. OSPF
Both sides must match the hello and hold timer.
For fast hello which the hello intervla is lower than 1 second, the hello is carried as 0. So the hello multipler dose not need to be match.


2. EIGRP
Two sides will exchange the hold time. It does not need to be matched. The router will use the hold time learn from the neighbor as the hold timer.
Let's say you configure R1 hello=10 Hold=60. R2 with default hello=5, hold=15.
On R1 show ip eigrp neighbor, it will should hold time 15 for R2.
On R2 show ip eigrp neighbor, it will should hold time 60 for R1.

3. BGP
Two sides will exchange the hold time. But the difference between EIGRP and BGP is, BGP will choose the small one as the hold time for both side. And if hello time is not configure, it will calculator from hold time.

IPV6 redistribution.

1. By default it won't redistribute the connect interfaces over which the source protocol is running.

To enable it, there is an option " include-connected"

ipv6 router rip 1
redistribute ospf 1 include-connected.

RIPv2

1. RIP v1 &2 has a maximum datagram size (with an eight-byte UDP header) of 512 octets. So it is up to 25 route entries (each is 20 bytes).

2. RIP v2 support authentication.

Simple password authentication: it will use the first route entry. So it leaves only 24.

MD5 authentication: it will use the first and last one. So it leaves only 23.

You need to configure the authentication under interface.

3. Unicast update.

By default RIP uses broadcast(v1) or multicast(v2) to send updates. To use unicast update, you need to enable the interface to be part of the network, then mark it as passive interface and finally configure neighbor.

Passive interface just makes the interface no sending out broadcast or multicast updates. But it will still listen to the updates.

AD and EIGRP

1. When receiving a new EIGRP update, Will it compare inside the EIGRP topology firstly and then AD?

Let's look at the sample.

10.1.0.0 learn from BGP and then redistributed into EIGRP on R1.

default-metric 10000 10 1 255 1500
distance 200 0.0.0.0 255.255.255.255 10
access-list 10 permit 10.1.0.0

Then R1 receives an new update from its neighbor R2 with 10000 1200 1 255 1500.

So from the eigrp topology perspective, the one redistributed from BGP has better metrci than the one from R2. But the AD for R2 is 170, and 200 for BGP. Which one is prefer????

Answer, it prefers the AD first. So in R1's routing table, 10.1.0.0 is from EIGRP instead of R2.

Redistribution

1. EIGRP.
Distance command only works for internal routes, not external routes.
You can only change AD for all prefix at one.

BGP tips

1. Timer
When a connection is started, BGP will negotiate the hold time (only) with the neighbor. The smaller of the two hold times will be chosen. The keepalive timer is then set based on the negotiated hold time/3 and the configured keepalive time, which one is lower.

By default, keepalive is 60 sec and hold time is 180 sec.

R1(Confg)# neighbor R2 timer 10 40
On R1, when you do a show ip bgp R2, it will show keepalive 10 sec and hold time 40 sec.
On R2, when you do a show ip bgp R1, it will show that the keepalive is 13 sec(40/3) and hold time is 40 sec.

R1(Confg)# neighbor R2 timer 80 180
On R1, when you do a show ip bgp R2, it will show keepalive 60 sec(180/3) and hold time 180 sec.

OSPF

1. VL and area 0 range.

If an area is capable of carrying transit traffic (i.e., its TransitCapability is set to TRUE), routing
information concerning backbone networks should not be condensed before being summarized into the area. Nor should the advertisement of backbone networks into transit areas be suppressed. In other words, the backbone’s configured ranges should be ignored when originating summary-LSAs into transit areas.

To show if the area is transitCapability, do
R1# show ip ospf
=================
Area 1
Number of interfaces in this area is 1
This area has transit capability: Virtual Link Endpoint
Area has no authentication
SPF algorithm last executed 01:29:49.932 ago
SPF algorithm executed 13 times
Area ranges are
Number of LSA 12. Checksum Sum 0x052BF3
Number of opaque link LSA 0. Checksum Sum 0x000000
Number of DCbitless LSA 0
Number of indication LSA 0
Number of DoNotAge LSA 0
Flood list length 0
========================================

After you enable the virtual link, the "area 0 range" won't works (only for backbone area0).

To fix it, do not use virtual link, instead you can create a GRE tunnel and set it to area 0.

2. VL and GRE Tunnel
Virtual-link:
-It is considered part of (Area 0) by default, without any additional configuration.
-It dose not require any kind of addressing.
-Configuration is only needed under the OSPF routing process.
-Only routing updates are tunneled into the virtual-link, but data traffic is not.
-Transit area can not be a stub area.
GRE tunnel:
-Tunnel interfaces must be created and addressing is required. (can be unnumbered).
-Tunnel Address must be advertised into (Area 0) using a network command.
-Both routing updates and data traffic are tunneled; this introduces more overhead.
-Transit area can be any type; this means its your only option if the transit is a stub area.

3. Default route. Link.
You can not redistribute default route into ospf. It can be inserted into the OSPF domain only as an external or inter-area (summary) route. There are only two ways to generator default-route into ospf by:
a. default-information originate
b. summary only in stub or nssa. (you cannot do 'area 0 range 0.0.0.0 0.0.0.0)

RIP

1. RIP summary
RIP dose not support super net summary.

2. RIP default route
You can specific which interface should the default route sending out using "default-route originate route-map Interface".

route-map Interface
match ip address 1 //only when there is a route match access-list 10 will it create 0.0.0.0/0
set interface e0/0 //it will only send update 0.0.0.0/0 out e0/0

3. Filter routes
distribute-list 1 in e0/0

distribute-list prefix-list allow-nets in e0/0

distribute-list gateway all0w-source in e0/0 (Gateway is the ip address of the neighbor whom you receive a routing update).
The following prefix-list works with distribute-list gateway to only allow updates from 150.1.1.2.
ip prefix-list allow-source deny 150.1.1.1/32
ip prefix-list allow-source permit 150.1.1.2/32

4. Redistribute need to manually set the metric.

5. Troubleshooting tool
debug ip rip
will show you all the update sent and received.