Re: What does zero-successor mean?

starjake2002 · ‎05-24-2003

hi!

P 172.30.20.0/24, 0 successors, FD is 28416

via 172.30.250.1 (2279168/1767168), Serial0

via 172.30.250.189 (2279168/1767168), Serial1

via 172.30.250.5 (2279168/1767168), Serial2

via 172.30.252.2 (28416/2816), FastEthernet0

I think there is a successor via FastEthernet0....

What kind of problems can cause that result.

j-block · ‎05-29-2003

From the information given, the topology is not clear. Could you please elaborate on the same? I also think that there should be a successor since the FD is given, usually 0 successors are seen when the FD is Inaccessible. As far as IPX is concerned, a topology table entry will have zero successors when it is attached, but not in the router subcommand network list. The router has at least one neighbor announcing this network. This will usually be observed when the no redistribute rip command is issued.

starjake2002 · ‎05-30-2003

Thanks a lot for your reply.

Let me explain our network topology.

All routing protocol is eigrp.

NO redistribution from any other protocols.

Here our topology is...

---------------------------------------------------------------------------------------

router_B(7513) - wan - router(4500) - L3sw_B(3550) -| vlan(C,D)

|

(fddi, FE)

|

router_A(7513) - wan - router(4700) - L3sw_A(3550) -| vlan(A, B)

---------------------------------------------------------------------------------------

The symptom what I wrote was happend in router 4700...

and the router_a(7513) couldn't reach vlan A via router 4700

but could reach vlanB...

There is nothing physical difference between vlanA and vlan B.

Router_A(7513) had been advertised from router_B(7513) about vlan A and B.

We solved this problem by issue command 'no auto-summary'.

But this network has same network class(B class, ex; 192.168.x.x)

so, I think the command is not perfect solution of this case.

Because eigrp doesn't summarize on the same network, right?

But I just think the command had a affect on the establishing the neighbor

of the each routers.

In fact the neighbor table reestablished after the command had been issued,

and the route(4700) could find the neighbor.

I hope this can make sense to solve the problem.

I'm anticipating your reply.

Thank you.

starjake2002 · ‎06-02-2003

Let me correct my syntax...

"Router_A(7513) had been advertised from router_B(7513) about vlan A and B." -----> VlanA is advertised via router_B(7513) because L3sw is cross-connected with router4500 and router4700 via 10MB Ethernet and router(4500) advertized to router_b(7513) about vlanA.. But VlanB is advertised via router4700 so router_A(7513) can reach vlanB via router4700.

j-block · ‎06-03-2003

Hi,

I agree with you that when 'auto-summary' is tuned on, EIGRP will not

summarise the subnets belonging to the same major net. This command

is necessary only for enabling/disabling summarization for different major

networks. However, I am not sure if this affects neighbor discovery.

Please furnish some more details. Here's what I need to know:

1. Could you elaborate on the physical connection 'L3sw is cross-connected

with router4500 and router4700 via 10MB Ethernet ' .

2. Could you also provide the Subnet IDs being used for the various links (

You could use Private IP to illustrate the same )

3. The topology table for 4700 in the initial question of yours shows the

route 172.30.20.0/24 being learned via 4 interfaces, but this is not

evident from the topology given by you now. Also the subnet on which

192.16.x.x network is being used.

ruwhite · ‎06-03-2003

> I agree with you that when 'auto-summary' is tuned on, EIGRP will not

> summarise the subnets belonging to the same major net. This command

> is necessary only for enabling/disabling summarization for different major

> networks. However, I am not sure if this affects neighbor discovery.

Autosummarization has no impact on neighbor formation.

:-)

Russ W ..

ruwhite · ‎06-03-2003

BTW--i'm not certain what the original question was here. The topic line says "what does a zero successor mean?" A zero successor route is a route that is in the eigrp topology table, but there is no successor, which means no route is installed based on this topology table entry. The most common reason for this condition is there's another route in the routing table with a lower administrative distance.

:-)

Russ W ..

starjake2002 · ‎06-03-2003

Hi

First of all, I'm very thankful for your reply....

Um... When I issued the command 'no auto-summary', I found that the neighbors are reestablished. I verified with the command 'sh ip eigrp neighbor'.

-------------------------------------------------------------------------------------------------------

And There was a successor in the topology table as you've seen.

Although the table get the successor, the topology could not adapt as a successor. I don't know why this kind of symptom can happen. There is no routing table with a lower administrative distance.

The Origial question is this.. There is a successor but topology can not adapt the successor as a real successor and advertise to other routers what I don't have any successor. But you know, there is another subnet(172.30.21.x) is working well. Only (172.30.20.x) is not working properly. This is my question.

---------------------------------------------------------------------------------------------------------

And the 4700 has one FastEthernet and one Ethernet... Each of them is connected to 3550A and 3550B.. also 4500 has same like this....

--------------------------------------------------------------------------------------------------------

There are 4 subnets... From 172.30.20.x to 172.30.23.x... and 192.168.x.x is just example network we don't have...

4-Links what I found are the link the 4700 has found via 7513_A. Infact there shoud be just one link to 172.30.20.x subnet via FastEthernet and I don't think other 3 links are has lower administrative distance or better metric...

Jake Lee...

ruwhite · ‎06-06-2003

Okay:

-- The status of auto-summarization has no bearing on building adjacencies.

-- I don't think you've provided enough information with regards to what is in your routing table, or what routes you are talking about having a successor, or feasible successor.

My suggestion is that you open a TAC case, since the amount of information required is going to be too much to handle in a forum of this type.

Russ

starjake2002 · ‎06-15-2003

Hi...

I really want to know what kind of situations can happen '0 successor' in eigrp neighbor table even if there is a path has FC is satisfied as a successor.

Anybody know about this?

ruwhite · ‎06-15-2003

The only valid situation I know of is if EIGRP and some other protocol attempt to install the same route in the routing table, and EIGRP has the higher admin distance. To see this, advertise some route to a router running eigrp, then create a static for the same route on the router receiving the route through eigrp. Don't redistribute static routes or anything, just look at show ip eigrp topo zero.

You should see the route in there with zero successors. There are bugs where this can occur, but I don't know of any currently in the code (they've all been fixed).

Russ.W