Question about routed connections

Answered Question
Jul 21st, 2007

The set up I have now is the followng:


I have a router running eigrp whose FastE interface is conencted to an ethernet port on a catos switch. That catos switch's MSFC is also running an instance of eigrp. Both devices are exchanging eigrp updates.


Here are the specifics:


Th FastE interface of the router has an IP address within the range of vlan 38. Vlan 38 is configured, along with its SVI, on the L3 switch, too. The eigrp process on the MSFC has, of course, the "no passive interface vlan38" command configured to allow routing updates to pass through to the router and back...


Now that L3 switch is going to have its MSFC disabled and perform only L2 switching. Furthermore, that switch will be trunked up to an IOS distro switch with the SVI for vlan 38 configured on it. In other words, the L3 duties originally being performed by the catos switch have been migrated UP to a new distro switch, which is running IOS, not catos.


So, to for the router to continue to be able to exchange eigrp updates within the new environment, that router connection must be migrated up to the new distro switch (lets say to interface gigabitethernet 3/1) and then that ge3/1 interface must be allowed to pass eigrp updates with the "no passive interface" command on the IOS switch's eigrp process.


Am I right? Or is it sufficient to keep the router connected to what will become the L2-only switch, as long as vlan38 is allowed on th etrunk? I dont think the latter is correct.

Correct Answer by royalblues about 9 years 7 months ago

Absolutely


Narayan

Correct Answer by deepinder about 9 years 7 months ago

Hi,


There is no need to change the physical connectivity, if Router can be reached from int vlan 38 on MSFC.


For peers to form eigrp neighbors they should be able to reach each other directly so that eigrp multicast/unicast packets can be exchanged. In ur case vlan38 will be considered as one broadcast network spanning accross multiple switches. So Eigrp peers would be able to talk to each other.


Please rate this if the info was of any use.


Thanks


Deepinder Singh Babbar

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Correct Answer
deepinder Sat, 07/21/2007 - 23:41

Hi,


There is no need to change the physical connectivity, if Router can be reached from int vlan 38 on MSFC.


For peers to form eigrp neighbors they should be able to reach each other directly so that eigrp multicast/unicast packets can be exchanged. In ur case vlan38 will be considered as one broadcast network spanning accross multiple switches. So Eigrp peers would be able to talk to each other.


Please rate this if the info was of any use.


Thanks


Deepinder Singh Babbar

lamav Sun, 07/22/2007 - 10:58

OK, I think I understand. You are saying that, because the router has connectivity over the trunk uplink to the L3 switch's SVI interface (for vlan 38), both devices are able to establish an adjacency (neighbor relationship) and begin exchanging routes.


Do I have it right?


Ok, so, if this IS true, then do I have to configure a "no passive interface" command under the L3 switch's eigrp process for the interface that supports the vlan trunk?

royalblues Sun, 07/22/2007 - 11:32

passive interface would be required only for the SVI i.e VLAN 38 in your case


Narayan

lamav Sun, 07/22/2007 - 11:42

Of course. What the ^%$#@! was I thinking??? The trunk is an L2 connection and has nothing to do wtih allowing eigrp neighbors to be established or routes to be exchanged. Its ROUTED intrfaces that one must be concerned with...correct?



lamav Sun, 07/22/2007 - 11:59

Deepinder and Narayan, thank you to the both of you for your help.


I gave the both of you credit for giving the right answer -- I hope I did it right.

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