OSPF question

[eiregobragh]

Guys,
just a problem I have with understanding/ implementing OSPF. I've a 3845 router with a fibre uplink on gi 0/0/0 to a 4507R Switch.

The switch has 9 vlans with their own subnets.

For the Router to see those vlan subnets do I need to issue the command on the 4507R:

redistribute connected subnets

I was under the impression that once two ospf neighbors in the same area establish an adjacency they will synchronise routing tables????

Thanks,

Paul

Paul Kilcoyne B. Eng.
Innealtóir/ Engineer

http://www.pknetworks.ie

 

[ISPKing]

Nope you got it right. You need to Add those sub-nets in by
redistributing the connected and statics respectively.

CCNP

 

[Cluebird]

Watch your MTUs between the router and switch. Routers set the MTU to 1500, while switches often set the MTU to a larger value to accommodate tags. In this situation, the OSPF neighborship won't form. You can either change the MTU manually or tell the router to "ip ospf mtu-ignore".

 

[ISPKing]

do a sho system mtu to double check what cluebird said.

CCNP

 

[Quadratic]

I agree with the above but also advise caution on using 'ip ospf mtu ignore'. Best to get the MTU straight than set OSPF to ignore it. Here's an article worth reading if you do choose to go that route:

http://blog.ioshints.info/2009/11/ip-ospf-mtu-ignore-is-dangerous-command.html

CCNP, CCDP

 

[eiregobragh]

Guys,
I've been talking with a colleague and he believes that the following should suffice to include all Vlans/Subnets on my 4507R switch:

router ospf 100
network 10.26.16.0 0.0.3.255

that covers the subnets in my vlans that I want to advertise to the Router, therefore the "redistribute connected subnets" command is not necessary.

Am I right here?

Thanks again,

Paul

Paul Kilcoyne B. Eng.
Innealtóir/ Engineer

http://www.pknetworks.ie

 

[unclerico]

You said originally that you had 9 subnets that statement will advertise only four of them. Your colleague is correct. One thing I do on switches with large amounts of subnets is add the command passive-interface default and then specify no passive-interface <inteface_name> for interfaces that need to form neighborships with other devices.

I hate all Uppercase... I don't want my groups to seem angry at me all the time! =)
- ColdFlame (vbscript forum)

 

[Cluebird]

Don't forget the area in the network statement.

router ospf 100
network 0.0.0.0 0.0.0.0 area 0
router-id 1.1.1.1
passive-interface default
no passive-interface vlan 10
no passive-interface vlan 11
no passive-interface vlan 12
no passive-interface vlan 13
no passive-interface vlan 14
no passive-interface vlan 15
no passive-interface vlan 16
no passive-interface vlan 17
no passive-interface vlan 18

HTH