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New Member

even more on routing

Hi all,

I think i am getting more confused by the day. Given the following ( as i am sure you remember by now!)

internet

|

CE1 - - PE1- - - -PE2 - - -CE2

|

|

CE3- - internet

My CE1 location is my headquarters. at this location i have the wan router, then connected to a core switch, which then goes to my firewall. my question being, if am running BGP at this wan router how do handle the default routes? i learned yesterday from the ISP that i need to be doing loopback address peering with them. currently i have a default route from my wan router to my core switch as all my servers reside locally at CE1. I am confused as currently I have the following:

ip route 0.0.0.0 0.0.0.0 <core switch>

ip route <remote net> <edge router>

ip route <remote net> <edge router>

As you can see I have static routes for all of my traffic pointing directly to my edge router of my isp. If i am running bgp with the new service provider i assume i will be doing something like the following?

router bgp 2386

neighbor <PE router> remote-as 65002

neighbor <PE router> route-map SetPref out

neighbor <PE router> send-community

neighbor <PE router> update-source Loopback0

default-information originate

no auto-summary

!

ip route <PE Loopback0> 255.255.255.255 <PE router>

ip route 0.0.0.0 0.0.0.0 <core switch>

ip route <remote net> <PE Router>

ip route <remote net> <PE Router>

ip route <remote net> <PE Router>

!

access-list 1 permit 0.0.0.0 0.0.0.0

!

route-map SetPref permit 10

match ip address 1

set community 7018

set local-preference 100

Am i to leave the default route of 0.0.0.0 in place to the core switch? and do i need all of these static routes to my remote nets as i am using bgp?

TIA,

R

1 ACCEPTED SOLUTION

Accepted Solutions
Purple

Re: even more on routing

Ok, I think I get what you mean now.. since the default route on CE1 points to your switch, you are asking why you need to redistribute that particular route ? The answer to that question is that when you redistribute that route into BGP, the PE routers will only know that the default route leads to the CE1 WAN router - any information about where that static route was initially pointing at. The default route received by the PE routers will have the CE1 WAN router's WAN IP address as the next-hope.

HOpe that was it.

Paresh

12 REPLIES
Purple

Re: even more on routing

Hi Mate,

Firstly, since you will be peering with your p's loopback, you will need this one additional command under 'router bgp 2386':

neighbor ebgp-multihop

If you don't do that, your BGP packets will get sent with a TTL of 1, which will then get dropped at the provider.

Nextly, you certainly don't need the static routes to the remotes as this will defeat the purpose of using BGP. However, you should leave the static default route to the switch in place since that is how you will draw traffic from the remote sites. Also, you will need the following statement under 'router bgp 2386' to redistribute that static default into BGP:

'redistribute static'

That command, together with 'default-information originate', will ensure that the default gets advertised via BGP.

Hope that helps - pls rate the post if it does.

Paresh

New Member

Re: even more on routing

Awesome, thanks again for your help.

One question, if I did not have the 'redistribute static' in my BGP config, would all of the other sites not still come to me as the PE routers know me(CE1) as the default route? and then the router would then send to my core because it is its default route? again, excuse my lack of knowledge! just trying to make sure i have a firm grasp moving forward for next time! i really appreciate all of your help!

Purple

Re: even more on routing

No proba again :-)

The 'redistribute static' is only to make sure that the CE1 router advertises the default out via BGP. If you have configured static defaults on the CEs, then this route is not required. The reason you do require it in your case is that you are injecting the default from two locations (CE1 and CE3) therefore both of these defaults must be known by the PEs so that it can determine when the primary one is down and then use the other.

Hope that helps - pls rate the post if it does.

Paresh

New Member

Re: even more on routing

ah, so you are saying this is needed so that the remote networks know that their info should not only go to the CE1 router but should also end up at the core switch at the CE1 location?

and you are also saying if I have other locations not participating in BGP, that a static route as follows:

ip route 0.0.0.0 0.0.0.0

would suffice?

Thanks!!

Purple

Re: even more on routing

In answer to your first question: no, that is not what I am saying. What I am saying is that you need to inject default routes into BGP from both CE1 and CE3. That way, the PE routers in the provider's core will know that there are two ways to get to the default route - as previously discussed, you can set the BGP attributes (AS-PATH prepending) such that the default route to CE1 is preferred over that to CE3. Now, if you do not advertise these routes via BGP, how are the provider PEs going to learn about them ?

The answer to your second question is: Yes, that is all that is needed at the remote locations. However, you still need to run a routing protocol at these sites to advertise their local networks to the PE routers (or get the PE router to use statics if your provider supports that).

Hope that helps - pls rate the post if it does.

Paresh

New Member

Re: even more on routing

to the first, i got the default route deal, but at the same time the route that my wan router has as its default route, i am still unsure as to why that has to be distributed as its internal to the CE1 network. only this local network uses this as a default route, so i was curious as to why the WAN would need this route as its default is the wan router at the CE1 location. does that make sense?

Purple

Re: even more on routing

Hmmm...not too sure I'm getting what you are getting at. You need to tell the provider's routers that the CE1 router offers a route to the Internet, and that is why you have to redistribute it. I'm probably still not getting your question here, mate...

Paresh

New Member

Re: even more on routing

i guess what i was getting is that as far as the PE router knows, CE1 is the route the internet. from there CE1 knows that its default route is my core switch. so why does the PE router need to know this? lol sorry for the frustration

Purple

Re: even more on routing

Ok, I think I get what you mean now.. since the default route on CE1 points to your switch, you are asking why you need to redistribute that particular route ? The answer to that question is that when you redistribute that route into BGP, the PE routers will only know that the default route leads to the CE1 WAN router - any information about where that static route was initially pointing at. The default route received by the PE routers will have the CE1 WAN router's WAN IP address as the next-hope.

HOpe that was it.

Paresh

New Member

Re: even more on routing

whew..yes, thats what i was getting at, hehe. i follow you now, i was having tunnel vision instead of seeing the bigger picture.

THANKS!!

Purple

Re: even more on routing

No probs... I guess it's just something I take for granted !

Paresh

New Member

Re: even more on routing

yes...you are wise in the ways of the cisco and routing. haha...it can get hairy when you are just starting! thanks again!

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