VLAN to VLAN Communications

Answered Question
Nov 19th, 2007

On our 4510 switch we have multiple VLANs. Two of the VLANs have IP addresses assigned to the VLAN interface. I assumed that no inter-VLAN communication would take place until I used the 'ip routing' command. That's not the case though. I do have communications between the two VLANs without this statement in place. We are using static routes but it does build the route to the directly connected interface. We also do not have a default route set on the switch.

From the documentation that I have read, you would need to enable 'ip routing' to route between VLANs but this doesn't seem to be the case.

Can someone clarify why this is happening?

Thanks!

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Correct Answer by gchabannas about 9 years 3 weeks ago

Your ip routing is enable ;)

As already said , the ip routing is on by default and depending on the equipement , you not see the ligne no ip routing or ip routing.

Gregory

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ryanparr9 Mon, 11/19/2007 - 09:56

Here is the output:

4510#show ip route

Codes: C - connected, S - static, R - RIP, M - mobile, B - BGP

D - EIGRP, EX - EIGRP external, O - OSPF, IA - OSPF inter area

N1 - OSPF NSSA external type 1, N2 - OSPF NSSA external type 2

E1 - OSPF external type 1, E2 - OSPF external type 2, E - EGP

i - IS-IS, su - IS-IS summary, L1 - IS-IS level-1, L2 - IS-IS level-2

ia - IS-IS inter area, * - candidate default, U - per-user static route

o - ODR, P - periodic downloaded static route

Gateway of last resort is not set

C 192.168.128.0/24 is directly connected, Vlan300

C 192.0.0.0/16 is directly connected, Vlan1

Thanks,

Ryan

gchabannas Mon, 11/19/2007 - 10:13

Are you sure the ip routing is disable ?

Because when it's disable :

Router#show ip route

Router#show ip route

Codes: C - connected, S - static, I - IGRP, R - RIP, M - mobile, B - BGP

D - EIGRP, EX - EIGRP external, O - OSPF, IA - OSPF inter area

N1 - OSPF NSSA external type 1, N2 - OSPF NSSA external type 2

E1 - OSPF external type 1, E2 - OSPF external type 2, E - EGP

i - IS-IS, L1 - IS-IS level-1, L2 - IS-IS level-2, ia - IS-IS inter area

* - candidate default, U - per-user static route, o - ODR

P - periodic downloaded static route

Gateway of last resort is not set

Router#conf t

Enter configuration commands, one per line. End with CNTL/Z.

Router(config)#no ip routing

Router(config)#exit

Router#show ip rout

Default gateway is not set

Host Gateway Last Use Total Uses Interface

ICMP redirect cache is empty

Router#

there is a difference.

Gregory

ryanparr9 Mon, 11/19/2007 - 10:22

I guess I am not sure if it is disabled or not. I don't see 'ip routing' in my config so I assumed it wasn't enabled.

Is it safe to assume that it is enabled however since I do have VLAN to VLAN traffic?

I don't want to issue the no command to test since I am in a production environment.

Thanks for your help,

Ryan

glen.grant Mon, 11/19/2007 - 10:24

Ip routing is on by default on the 4500 series and you have to turn it off if you just want layer 2 .

Correct Answer
gchabannas Mon, 11/19/2007 - 10:34

Your ip routing is enable ;)

As already said , the ip routing is on by default and depending on the equipement , you not see the ligne no ip routing or ip routing.

Gregory

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