EIGRP Stub design question:

Answered Question

Hi - i have an issue, which i'm trying to get around without using static routes.

I have stacked 3750E's to my floors, which will be the L3 distribution layer. (I've had Cisco in here, and this is the design they pushed. Looks good, they're powerfull redundant switches).

The Floor Stacks are running 'ipbase' which support the EIGRP Stub.

I want it so the floors recieve a default route only, and have configured it as such. (eg, eigrp stub, network 10.0.0.0).

I have statics configured on my 6509 cores, and they have ICMP access to everything.

In the diagram - the PC on the left cannot ping the PC on the right. If i configure statics on the stacks it comes straight up, but statics don't help me should i lose one of the cores.

Is my only solution, to get rid of my /30's and create a big HSRP domain?

Any suggestion helpfull. Thanks, - JH.

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Correct Answer by Jon Marshall about 9 years 3 months ago

James

You do not have a default-route on your 3750 pointing back to the 6500's and you also have all the P2P /30 subnets on your 3750'S which isn't right either.

All you want on the 3750 is the P2P /30's for that 3750 and the local vlans + a summary route for the rest of the network.

What you need to do is advertise a summary route from the 6500's switches to the 3750 swithes. You can do this in one of two ways

1) Have a default route on your 6500 and redistribute it up to the 3750's. Use a distribute list under the eigrp config on your 6500's to only allow the default-route to the 3750 switches.

If you already have a default route in your network this would work fine but if you don't and it looks like you don't from your 6500 routing table

2) On each of the interfaces on the 6500's that connect to the 3750's you need to add

ip summary-address eigrp 1 10.0.0.0 255.0.0.0

This will advertise a summary route to the 3750's.

NOTE - only thing i'm not sure as i have forgotten is if you use the "ip summary-address eigrp...." command does it suppress the more specific routes or do you still have to filter them out.

If no one else can confirm you could either test and check or i'll check in lab tomorrow.

** Please do this out of hours ie. not in production hours **

Does all of this make sense ?

Jon

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Jon Marshall Mon, 10/08/2007 - 04:19

Hi James

What do the routing tables on the 3750's show. Do you see a defautl route pointing back to the 6500's.

The design you have will work, we have deployed the same in one of our VOIP offices.

Be aware that the EIGRP stub feature only affects routes being advertised to the 6500's ie. you still need to advertise the default-route from the 6500's to the 3750's.

HTH

Jon

Thanks Jon.

On my 6509 i have:

Gateway of last resort is not set

10.0.0.0/8 is variably subnetted, 19 subnets, 2 masks

S 10.41.3.0/24 [1/0] via 10.30.254.5

S 10.40.2.0/24 [1/0] via 10.30.254.1

S 10.41.2.0/24 [1/0] via 10.30.254.1

S 10.40.3.0/24 [1/0] via 10.30.254.5

S 10.41.7.0/24 [1/0] via 10.30.254.21

S 10.40.6.0/24 [1/0] via 10.30.254.17

S 10.41.6.0/24 [1/0] via 10.30.254.17

S 10.40.7.0/24 [1/0] via 10.30.254.21

S 10.41.5.0/24 [1/0] via 10.30.254.13

S 10.40.4.0/24 [1/0] via 10.30.254.9

S 10.41.4.0/24 [1/0] via 10.30.254.9

S 10.40.5.0/24 [1/0] via 10.30.254.13

C 10.40.254.0/24 is directly connected, Vlan254

C 10.30.254.8/30 is directly connected, GigabitEthernet4/4

C 10.30.254.12/30 is directly connected, GigabitEthernet4/5

C 10.30.254.0/30 is directly connected, GigabitEthernet4/2

C 10.30.254.4/30 is directly connected, GigabitEthernet4/3

C 10.30.254.16/30 is directly connected, GigabitEthernet4/6

C 10.30.254.20/30 is directly connected, GigabitEthernet4/7

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

On my 3750E's:

Gateway of last resort is not set

10.0.0.0/8 is variably subnetted, 8 subnets, 2 masks

C 10.40.5.0/24 is directly connected, Vlan5

D 10.40.254.0/24

[90/3072] via 10.30.254.14, 00:05:15, GigabitEthernet1/0/49

D 10.30.254.8/30

[90/3072] via 10.30.254.14, 00:05:15, GigabitEthernet1/0/49

C 10.30.254.12/30 is directly connected, GigabitEthernet1/0/49

D 10.30.254.0/30

[90/3072] via 10.30.254.14, 00:05:15, GigabitEthernet1/0/49

D 10.30.254.4/30

[90/3072] via 10.30.254.14, 00:05:15, GigabitEthernet1/0/49

D 10.30.254.16/30

[90/3072] via 10.30.254.14, 00:05:16, GigabitEthernet1/0/49

D 10.30.254.20/30

[90/3072] via 10.30.254.14, 00:05:16, GigabitEthernet1/0/49

--------

EIGRP CONF ON 3750:

*** IP Routing is NSF aware ***

Routing Protocol is "eigrp 1"

Outgoing update filter list for all interfaces is not set

Incoming update filter list for all interfaces is not set

Default networks flagged in outgoing updates

Default networks accepted from incoming updates

EIGRP metric weight K1=1, K2=0, K3=1, K4=0, K5=0

EIGRP maximum hopcount 100

EIGRP maximum metric variance 1

Redistributing: eigrp 1

EIGRP NSF-aware route hold timer is 240s

Automatic network summarization is in effect

Maximum path: 4

Routing for Networks:

10.0.0.0

Routing Information Sources:

Gateway Distance Last Update

10.30.254.14 90 00:06:58

Distance: internal 90 external 170

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

EIGRP ON MY 6509:

*** IP Routing is NSF aware ***

Routing Protocol is "eigrp 1 1"

Outgoing update filter list for all interfaces is not set

Incoming update filter list for all interfaces is not set

Default networks flagged in outgoing updates

Default networks accepted from incoming updates

EIGRP metric weight K1=1, K2=0, K3=1, K4=0, K5=0

EIGRP maximum hopcount 100

EIGRP maximum metric variance 1

Redistributing: eigrp 1 1

EIGRP NSF-aware route hold timer is 240s

EIGRP NSF disabled

NSF signal timer is 20s

NSF converge timer is 120s

Automatic network summarization is in effect

Maximum path: 4

Routing for Networks:

10.0.0.0

Routing Information Sources:

Gateway Distance Last Update

10.30.254.13 90 00:08:49

10.30.254.1 90 00:08:49

Distance: internal 90 external 170

Correct Answer
Jon Marshall Mon, 10/08/2007 - 10:32

James

You do not have a default-route on your 3750 pointing back to the 6500's and you also have all the P2P /30 subnets on your 3750'S which isn't right either.

All you want on the 3750 is the P2P /30's for that 3750 and the local vlans + a summary route for the rest of the network.

What you need to do is advertise a summary route from the 6500's switches to the 3750 swithes. You can do this in one of two ways

1) Have a default route on your 6500 and redistribute it up to the 3750's. Use a distribute list under the eigrp config on your 6500's to only allow the default-route to the 3750 switches.

If you already have a default route in your network this would work fine but if you don't and it looks like you don't from your 6500 routing table

2) On each of the interfaces on the 6500's that connect to the 3750's you need to add

ip summary-address eigrp 1 10.0.0.0 255.0.0.0

This will advertise a summary route to the 3750's.

NOTE - only thing i'm not sure as i have forgotten is if you use the "ip summary-address eigrp...." command does it suppress the more specific routes or do you still have to filter them out.

If no one else can confirm you could either test and check or i'll check in lab tomorrow.

** Please do this out of hours ie. not in production hours **

Does all of this make sense ?

Jon

Jon Marshall Mon, 10/08/2007 - 12:20

James

Glad to have helped and appreciate the rating.

One thing however. Sundar makes a very good point about the static routes on the 6500 switches. You should not have these. The 3750's should be advertising their local vlans (and only their local vlans) to the 6500 switches.

Jon

Thanks Jon & Sundar.

I've seperated out each 'floor' to be a different EIGRP AS. Therefore:

(for AS 2) (2nd floor)

On 6509: (under gig int 4/2)

ip summary-address eigrp 2 10.0.0.0 255.0.0.0

(under gig int 4/3)

ip summary-address eigrp 3 10.0.0.0 255.0.0.0

and so on...

Router eigrp 2

Redistribute static ..?

Am i on the right track?

Thanks.

Jon Marshall Mon, 10/08/2007 - 12:28

James

You really want to keep the same EIGRP AS for all the devices.

Your summary addressing is fine and should work.

You will need to make sure that the 6500 is receiving advertisements from each of the 3750's for their local vlans ie. remove the statics from the 6500.

The command on the 3750's under the eigrp config

router eigrp 1

eigrp stub connected

This should advertise each 3750's local subnet to the 6500 + the P2P /30 link.

Jon

sundar.palaniappan Mon, 10/08/2007 - 11:56

James,

The problem you are having is due to the fact that you have static routes on the 6509 to all those VLANs which you aren't probably redistributing. You can use any one of those two solutions suggested by Jon but I would recommend using the 'ip summary-address eigrp' to keep the configuration simple. In the meantime if you are in hurry to find a interim solution then you can either redistribute the static on the 6509 or remove the static route(s) from the 6509.

HTH

Sundar

PS: James, I just saw your response posted mins ago. Glad to hear you've got a solution!!

Jon Marshall Wed, 10/10/2007 - 08:59

James

Glad to hear it's going well.

i assume you mean preferred default route from the 3750's. Well there is an option on the "ip summmary-address..." command where you can specify an AD (administrative distance). What you could do is specify a higher AD on one of the 6500 uplinks.

I would question why you want to do this though. One of the major advantages to a routed access-layer is that you can have 2 equal cost paths to the distribution switches ( your 6500's ) for all networks. To achieve this with layer 2 you have to configure additional settings for both STP and HSRP.

Is there any reason why you need to only have one path active at a time.

Jon

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