Testing shortly... review help from the memers of the audience

[NahRamp2]

Well i'm planning on taking the CCNA in the next 2 weeks... but there are a couple loose end questions that i need to find out. Maybe you guys can help. As i continue to refresh for the next 2 weeks, plan on creating threads with a few questions here and there.

Today's question:

When configuring the router, what is the purpose of the loop back device and why configure it?

 

[IllogicallyLogical]

The IOS uses the highest local active IP address as its OSPF router ID when the OSPF routing process starts. If there is no active interface, the OSPF process will not start. If the active interface goes down, then the process will not start until the interface comes back up. Configuring a loopback interface ensures OSPF stability because there will be an active interface at all times. When a loopback address is configured OSPF uses this as the router ID.

Joey
A+, Network+, MCP

 

[NahRamp2]

So, does that mean that only ospf requires the use of a loopback device? If not, what are some other reasons that you need to have a loopback device specified. And thanks of getting back to me so fast. I'm going to use this forum for my ccnp once i climb this mole hill

 

[IllogicallyLogical]

Looks like EIGRP uses the loopback interface in much the same way as OSPF. Check

http://www.cisco.com/warp/public/103/eigrp-dup-id.html

for more info.

Joey
A+, Network+, MCP

 

[burtsbees]

Any reason to keep a logical interface up---route maps, virtual templates, virtual access all use loopback interfaces, and like for example in a virtual-access config, it can use
router(config-if)#ip add unnumbered loopback 0
instead of statically defining an IP address. The correct answer is simple---to have an interface that is always up.

Burt