Loopback interfaces 3

[Almin]

Hi

Im douing a Lab on PPP but im not nderstanding the loopback part of that lab. Bellow I have the topology that the lab simulates, my question is thet ISP router is connected to interface Lo0, how should I cable that part straight to fe0/0?

and also what is the purpose of this, I read int he book that Loopback interfaces are supported on all platforms. A loopback interface is a virtual interface that is always up and allows Border Gateway Protocol (BGP) and remote source-route bridging (RSRB) sessions to stay up even if the outbound interface is down. The book realy does not talk about the purpose as much as it talks about stuff like IPX and Null 0 interfaces.

What would I want to set up a opback interface on my router at work?

thanks bellow is the link for the topology

http://www.mediafire.com/file/mrgznt4gm5y/Loopback.bmp

 

[burtsbees]

How do the two routers physically connect to eachother? Your default route would point to the other's loopback.

Loopbacks can serve several purposes---NAT (floating static routes where xlates must be cleared), management, ISP simulation in labs, OSPF DR/BDR selection...

/

tim@tim-laptop ~ $ sudo apt-get install windows
Reading package lists... Done
Building dependency tree
Reading state information... Done
E: Couldn't find package windows...Thank Goodness!

 

[Almin]

Well the question i should have asked is "How do i physicly connect the ISP router to router R2? I dont think that i have very many options fa0/0 and fa0/1. If I connect to eather one and create the loopback 0 what will that do exept for creating an Lo0 virtual interface. What would happen if the physical connection is fa0/0 and that int goes down what's going to happen with the Lo0?

Thanks

 

[VinceWhirlwind]

L0 can continue to communicate back through the other interface, which is handy because it can pass back the information that the first interface is down.

 

[Caspiansails]

Burtsbees is correct there are many uses for Loopback addresses. It is not true that using a loopback will keep a BGP association established if the intermediate path is down. For an EBGP neighbor you would want to use the directly connected interface for the neighbor, if not you can do some things with multi-hop but for EBGP in most situations using the ISP connected interface is the best choice. IBGP has some benefit of using the loopback scenario for route stability especially if you have multiple paths to the neighber. This is also true in the case of EBGP if you are attempting to use multiple physical interfaces to a EBGP neighbor - not a very common strategy and it does require using a few other BGP features to work effectively.

I think what they are looking for in this lab scenario is do you know the extra steps you need to perform to use the Loopback interface as the neighbor for an ISP connection instead of using the directly connected interface. You will remember it much better if you find the information yourself. There are a few gotchas for this and I ahve given some of the informatin earlier.

You cannot physically connect a loopback interface to another interface as the loopback is a virtual interface in the router.

You

 

[Almin]

Thanks guys

makes more sense now

I will play with it a litle

 

[burtsbees]

int fa0/0
ip unnumbered lo0
no shit
!
int lo0
ip add 209.165.200.225 255.255.255.224
!

/

tim@tim-laptop ~ $ sudo apt-get install windows
Reading package lists... Done
Building dependency tree
Reading state information... Done
E: Couldn't find package windows...Thank Goodness!