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New Member

Redistribution problems

I met a problem in real networks. The problem is that, a router with two serial interfaces and one ethernet interface, One serial interface joins the Eigrp, another serial interface with static route and the ethernet interface joins OSPF, I configured redistribution between EIGRP and OSPF, now i redistribute the static route into OSPF, the router's OSPF neighbor can learn the redistributed static, however the router's eigrp neighbor cannot learn the route. Then I redistribute the static into the Eigrp, this time the router's eigrp neighbor can learn the route, and it's OSPF neighbor have no such route. I wanna make sure that this status is normal, if i wanna make static known to both the router's eigrp and ospf neighbor, should i redistribute the static route into both dynamic routing protocols?

1 ACCEPTED SOLUTION

Accepted Solutions
New Member

Re: Redistribution problems

yes you should redistribute the static into both protocols

the status you are describing is normal ,

when you are configuring redistribution on a router remember the routes that are redistributed are the routes that are in the routing table of a router , i'll

make myself more clear with the following scenario ,imagine a different router than yours with 3 interfaces the first runs eigrp the second ospf and the third rip , both ospf and eigrp interfaces receive the following prefix 10.1.1.0/24 and you are redistributing ospf into rip , you will notice that the rip domain will not get the route and the reason is because although the ospf database has the route , ospf didnt inject it into the routing table because eigrp did with its lower distance. so the only way for rip to know the route is to redistribute eigrp into rip.

so lets now look into your scenario

you have redistribution between ospf and eigrp and you have a static route

so when you are doing redistribute static into ospf the ospf domain learns this route but eigrp doesnt because remember eigrp will get the ospf routes that are in the routing table and the static route is part of the ospf database but isnt in the routers routing table because the static is with its distance of 1 (ospf has 110) so eigrp will get the only the ospf routes that are actually installed in the routing table.

and the same thing will happenes vice versa if you redistribute the static into eigrp , ospf wil not get the static route because the route is in the routing table because of the static route and not eigrp that has a distance of 90

well hope this explanation isnt too long

good luck

guy

4 REPLIES
New Member

Re: Redistribution problems

yes you should redistribute the static into both protocols

the status you are describing is normal ,

when you are configuring redistribution on a router remember the routes that are redistributed are the routes that are in the routing table of a router , i'll

make myself more clear with the following scenario ,imagine a different router than yours with 3 interfaces the first runs eigrp the second ospf and the third rip , both ospf and eigrp interfaces receive the following prefix 10.1.1.0/24 and you are redistributing ospf into rip , you will notice that the rip domain will not get the route and the reason is because although the ospf database has the route , ospf didnt inject it into the routing table because eigrp did with its lower distance. so the only way for rip to know the route is to redistribute eigrp into rip.

so lets now look into your scenario

you have redistribution between ospf and eigrp and you have a static route

so when you are doing redistribute static into ospf the ospf domain learns this route but eigrp doesnt because remember eigrp will get the ospf routes that are in the routing table and the static route is part of the ospf database but isnt in the routers routing table because the static is with its distance of 1 (ospf has 110) so eigrp will get the only the ospf routes that are actually installed in the routing table.

and the same thing will happenes vice versa if you redistribute the static into eigrp , ospf wil not get the static route because the route is in the routing table because of the static route and not eigrp that has a distance of 90

well hope this explanation isnt too long

good luck

guy

New Member

Re: Redistribution problems

Thanks a lot for your explanation! I did experiment to verify the facts and it's actually works like what you said. And one more thing to consider is the necessity of avoiding the so-called routing loops, since i do two-way redistribution between eigrp and ospf, is there a possibility a route bounce back? if i need route map to filter the repeated route, in which side will be correct? Hope can get more help!

Thanks again!

Hao

New Member

Re: Redistribution problems

guy,

it seems to explain this issue..but imagine we have just two routing protocols running on a router..eigr and ospf..one interface is in eigrp and the other is in ospf..now if we configure mutual redistribution then the connected interface network should not be advertised becuase it is in the Routing table as connected not as either E or O route. so y does this information gets propagated ?

Gold

Re: Redistribution problems

Start with a route, say 208.0.4.0/24, connected to a router. You configure ospf to cover this interface:

router ospf 100

log-adjacency-changes

redistribute eigrp 100 metric 10 subnets

network 208.0.4.0 0.0.0.255 area 0

You then configure eigrp to redistribute ospf:

router eigrp 100

redistribute ospf 100 metric 1000 1 255 1 1500

network 208.0.6.0

auto-summary

And look in the eigrp topology table:

7206F#sho ip eigrp topo 208.0.4.0

IP-EIGRP (AS 100): Topology entry for 208.0.4.0/24

State is Passive, Query origin flag is 1, 1 Successor(s), FD is 2560256

Routing Descriptor Blocks:

0.0.0.0, from Redistributed, Send flag is 0x0

Composite metric is (2560256/0), Route is External

Vector metric:

Minimum bandwidth is 1000 Kbit

Total delay is 10 microseconds

Reliability is 255/255

Load is 1/255

Minimum MTU is 1500

Hop count is 0

External data:

Originating router is 208.0.10.4 (this system)

AS number of route is 100

External protocol is OSPF, external metric is 0

Administrator tag is 0 (0x00000000)

Note that eigrp picks the route up. This is because when ospf has a network statement for 208.0.4.0/24, it willmark the route in the routing table with information indicating that ospf "owns" this route. When eigrp examines the routes in the routing table, it will note that ospf "owns" this route, which appears to be the same thing as ospf learning the route, so it will redistribute it into eigrp.

Note that the 208.0.6.0/24 is covered by eigrp's network statements, and that ospf is redistributing eigrp. When we look at ospf's database, we see:

7206F#sho ip ospf data external

OSPF Router with ID (208.0.10.4) (Process ID 100)

Type-5 AS External Link States

LS age: 366

Options: (No TOS-capability, DC)

LS Type: AS External Link

Link State ID: 208.0.6.0 (External Network Number )

Advertising Router: 208.0.10.4

LS Seq Number: 80000001

Checksum: 0xF004

Length: 36

Network Mask: /24

Metric Type: 2 (Larger than any link state path)

TOS: 0

Metric: 10

Forward Address: 0.0.0.0

External Route Tag: 0

So, ospf is also picking up the eigrp route in the same way, from the routing table, and redistributing it.

Russ --

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