| Author |
ospf loopback addreses?
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| why do some routers have many loopback addresses?
thanks | |
| defcon1111 2002-04-02, 4:57 pm |
| the loopback address can be set for many reasons such as Designated and backup designated router elections. That is the biggest use i have seen so far, but have a long way to go before i understand it all | |
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This link may be useful,,,,,,,,, then again, it might just be REALLY confusing. I'm not going to begin to understand it; I'm nowhere near this level yet but, it does show multiple loopback addresses.
Have fun
http://www.cisco.com/univercd/cc/td...rt3/1cdmsdp.htm
Hippo (Sometimes night shifts are fun, , then some are SO boring,  ) | |
| supergoku0 2002-04-04, 12:26 am |
| For me I don't even understand the practical use of a loopback interface, let alone multiple ones...  Can somebody suggest some of its simple applications?
Thanks in Advance,
Goku | |
| kbani 2002-04-04, 12:50 am |
| Loopback int's have a couple of good uses, and it's not a difficult subject. If it is important to have a particular router become the DR or BDR in an OSPF environment the loopback address is very useful. It is also useful in a lab environment as it can simulate other networks, specially for access-list labs
you can do a extended ping and have one of the loopback network be the source or destination of that ping. It can also be used for address translation, or termination point for BGP, DLSW+, RSRB. Loopback interface is really nothing more then a virtual interface(software based). | |
| peterd 2002-04-04, 2:00 am |
| Hi,
I've set up several router here and sent them to remote sites for non-techies to install. I set up a loopback address so that I could telnet to the router even if the ethernet cable isn't plugged in correctly.
People have told me it's possible to get access to a remote router even if the ethernet isn't connected, but I've never managed to do it any other way than via a loopback address.
Regards
Peter | |
| supergoku0 2002-04-04, 3:04 am |
| Sorry that still I am not so clear how a loopback interface can help in your scenario above...
What subnet mask can be used for the loopback adddress? If the non-techies have plugged in the ethernet improperly are you saying we can telnet to the router thru' other interface say V35 i/f? Are there some other commands required apart from simply setting up a loopback interface?
TIA,
Goku | |
| Yankee 2002-04-04, 4:07 am |
| quote:
Originally posted by peterd
Hi,
I've set up several router here and sent them to remote sites for non-techies to install. I set up a loopback address so that I could telnet to the router even if the ethernet cable isn't plugged in correctly.
People have told me it's possible to get access to a remote router even if the ethernet isn't connected, but I've never managed to do it any other way than via a loopback address.
Regards
Peter
One reason not to do what you are doing is the size of your routing table. If you have a large international network you probably don't want to be advertising an extra network per router for a loopback used just for telnet.
If you can reach the loopback address it means your WAN connection is up so you should be able to telnet to the serial interface of the remote site (providing you are advertising it). I also deal with a ton of remote sites and we provide a modem to each site so we can dial in and look if the site hooks up something wrong or the carrier has screwed up the T1.
The primary purpose of a loopback int for OSPF is router identification and it is preferred due to its stability because it never goes down unless the router does.
Hope that helps a little,
Yankee | |
| Yeti-GBR1 2002-04-04, 4:15 am |
| Ah sense at last nice one Yankee  | |
| MadChef 2002-04-04, 5:55 am |
| quote:
Originally posted by Yankee
One reason not to do what you are doing is the size of your routing table.
And there is your reason for taking advantage of OSPF's summarization capabilities.
I always set up loopback addresses on all my layer 3 devices. I use a single subnet per area and address each device with a 32 bit mask. I use the loopback for dlsw peering, ntp source, snmp source, telnet source, etc. I have hostnames resolve to the loopback address.
Why would you have more than one loopback address? Mostly to generate additional routing entries in a lab scenario.
MadChef | |
| peterd 2002-04-04, 6:21 am |
| Hi guys,
I agree that my method wouldn't be pactical on a large network but it works on 7 sites using EIGRP.
Supergoku0: yep, not so much that they may have plugged it in wrong, but maybe the ethernet isn't yet 'up' at the far end (maybe waiting for a new hub, etc) and I want to prove that I have a WAN connection to the new router. I would be connecting from my site to the new router via the serial port.
If there's nothing on the ethernet port then it shuts down and I can't telnet onto it. A loopback address, being virtual, never shuts down...no matter what the morons at the far end do to their pc's, hubs, etc.
regards
Peter | |
| supergoku0 2002-04-04, 8:47 am |
| Cheers guys | |
| defcon1111 2002-04-04, 10:21 am |
| Thanks all i just learned a great deal and this is why i come here. you guys rock!!!! | |
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| MadChef 2002-04-04, 8:33 pm |
| quote:
Originally posted by Yankee
Everyone should be lucky enough to work on a MadChef designed network!
I'll say! Let me personally offer my services to any entity located in:
a) a tropical paradise with pristine beaches and excellent snorkeling
or
b) a rugged mountain wilderness with exceptional trout and/or salmon fishing opportunities
Seriously, a great deal of my work involves going into places that have grown chaotically over the years and whipping them into shape by migrating them to a logically designed network. Would I institute the same practices (setting up loopbacks everywhere) if I was working on Yankee's somewhat hodge podge network? Not without a very compelling reason. The need to maintain services like BGP and DLSw peers over multiple paths would be about the only thing to move me that direction.
I guess that's the difference between being in a position to design networks and primarily having to support an existing network. Throwing in loopbacks in Yankee's case (without a very strong reason to do so) is likely only going to make things more complicated.
MadChef | |
| Yankee 2002-04-06, 11:36 am |
| My network ain't that bad and there are no compelling reasons to use loopbacks that I can think of. We use EIGRP, don't support DLSW and only use BGP the couple of places where we peer with our providers.
I had pondered using them for DNS resolution for the remote site routers, while I still think it's a neat idea for some networks, mine doesn't need all the extra route entries (and don't say summarization again!) cuz there are other factors I won't go into now.
Here I fight the little battles, chipping away at problems before they become major issues. Stuff that can bring down networks and keep people like MadChef gainfully employed
Yankee |
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