Fixing EIGRP routes from Destination back to source

[mahesh18]

Hi Everyone,

Users need access to particular server.

I was checking the path from source Which is user PC gateway to Server.

Source 172.24.35.x----------------SW1

Server 172.23.7.0-------------------SW4

Here is info

Sw1 ------Sw2------Sw3-----Sw4

SW1 is user PC gateway and Sw4 is server gateway.

All the switches learn route via EIGRP.

SW1---EIGRP nei vlan 611---Sw2---tunnel148 Eigrp nei-----Sw3-----Eigrp nei vlan 611-------Sw4

I check the routing it is there from SW1 to Sw4 all the way.They are all learning routes via EIGRP.

When i check the reverse path from SW2 to source 172.24.35.0 it is not in EIGRP routing table.

Also when i check the reverse path from Sw4 to source 172.24.35.0  it points to different IP.

My question is to fix the  EIGRP routing back from Sw4  to Sw1 should i start from SW4   or SW2?

Which switch should i choose first to fix the EIGRP routes from SW4 back to SW1?

Regards

Mahesh

[Jon Marshall]

Mahesh

You don't mention whether SW3 sees the route back or not ?

Generally to propagate the route you start closest to the source so you would first need to look at SW1 to see if it has been included in the EIGRP configuration. If it has then move on to SW2 etc.

However you also say SW4 does see the route but sees a different next hop. Is this next hop not SW3 ?

If so I would first look at where SW4 is learning that route from and why it is learning it from there.

What is the next hop that SW4 is using ?

Jon

[mahesh18]

Hi jon,

SW3 sees route back to 172.24.35.0 via SW4.

SW4 is learning route back to 172.24.35.0 via different path.It is not SW3.

When i try to ping that next hop IP from Sw4 it is not reachable.

Also i found that interface on sw4 that points to different path is admin down.

So it means i can forgot about this path from SW4.

Now my only option is to fix the routing back from SW4 to SW1.

Should i start from Sw2 and put static route back to 172.24.35.0 pointing to SW1?

Regards

Mahesh
 

[Jon Marshall]

Mahesh

If the interface on SW4 is admin down then there should not be a route for it. You need to clear that first ie. work out why the route is still there.

Is this an EIGRP or a static route ?

Once you've cleared that then you need to work out why SW2 is not receiving an EIGRP route  so you need to check SW1's EIGRP configuration.

I'm assuming you want to get this working with EIGRP and not statics ?

Jon

[paul driver]

apologies Jon

didnt see your post

on my iphone - didnt refresh!

[Jon Marshall]

No problem, always good to have your input.

Jon

[mahesh18]

Hi Jon,

Yes Sw3 has static route back to Sw4 for return traffic.

Also Sw4 has static route back to 172.24.35.0.

I have cleared those static routes from Sw3 and sw4 for return traffic.

Then i checked the config of SW2 again.

It had no route back to 172.24.35.0.

So on Sw2 i added the static route

ip route NET 172.24.35.0 255.255.255.0 172.24.254.1

where 172.24.254.1 is EIGRP NEI VLAN 611 of SW1.

Once i did i can see that this route is advertised to SW3 and SW4 as EIGRP external route.

Now users connected to Sw1 can reach the Server connected to SW4.

So does it mean that for return path we should check the routing from near source first i mean to say SW2??

Best Regards

MAhesh

[Jon Marshall · Accepted solution]

Mahesh

Why did you need to add a static route on SW2 ?

If SW1 and SW2 are running EIGRP between them then you have just added complexity to the configuration. Imagine another network engineer looking at this and wondering why that static is there when it should be an EIGRP learned route.

I would recommend you  work out why that route is not being advertised with EIGRP rather than using a static.

In terms of working out where the routing has failed always start with traceroute because that should highlight where the issue is.

Jon

[mahesh18]

Hi Jon,

I totally agree with what you said.

Thanks for all the inputs.I will certainly look for why SW1 not advertising route

172.24.35.0 back to Sw2.

Regarding Traceroute it is not allowed in this customer environment  thats the reason it is very complicated here.

Best Regards

Mahesh

[Jon Marshall]

Regarding Traceroute it is not allowed in this customer environment  thats the reason it is very complicated here.

Ah, I can see why you were asking about that now.

In that case technically it really doesn't matter which end you start from. You just need to make sure on each router there is a route for both the source and destination subnets and that they are pointing to the correct next hops.

I would probably start on the router connected to the source network and go from there.

In a large network it could be very time consuming though :-)

Jon

[mahesh18]

Thanks for answering the question Jon !

[paul driver · Accepted solution]

hello

"So it means i can forgot about this path from SW4."

no you cannot as the switch still sees this route for some reason as still valid

is this a static route by any chance -you need to find out why and where sw4 is learning this invalid route

sh ip route 

sh ip eigrp neigbours

res

paul