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BGP configuration Verification Please-need to turnup today!

m-abooali
Level 4
Level 4

Hi,

I have come up with two BGP configuration for two border routers 6506 with two different ISPs, Multihomed. I have made it to recice default routes from both ISPs and advertise our blocks out to them and do load sharing at the same time plus redundancy in the event one ISp connection is down.

I have attched both files with the IPs half deleted! My time is very short, i.e. tomorrow or just today (Its 4:15 a.m. now!) and need to see if I have done alright. I have used IP prefix-list.

Also, I have a block with /21 mask and /20 mask and blocks with /20 and /19 (which is good for redundancy) I don't know if I have to break the /21 or it is OK as I have already listed in the Ip prefix-list statements.

/20 must be a sub-set of /21 and this is how Ihave thought about it!

Please advise.

Regards,

Mike

17 Replies 17

Harold Ritter
Cisco Employee
Cisco Employee

Masood,

I see you are advertising 216.x.224.0/19 and 216.x.224.0/20 from both routers. The strategy usually consists of sending the /19 from one router and the /20 from the other router, which would ensure both redundancy and load-balancing. BTW, you already do it the proper way for 216.y.192.0/20 and 216.y.192.0/21.

Also, make sure you have routes, matching the network statements, that are installed in the RIB.

Regards,

Harold Ritter
Sr Technical Leader
CCIE 4168 (R&S, SP)
harold@cisco.com
México móvil: +52 1 55 8312 4915
Cisco México
Paseo de la Reforma 222
Piso 19
Cuauhtémoc, Juárez
Ciudad de México, 06600
México

Masood,

One more thing. I noticed you are advertising 209.z.122.64/29. Service Providers will usually not propagate prefixes with a prefix length longer than 24. So this will definitely be an issue.

Regards,

Harold Ritter
Sr Technical Leader
CCIE 4168 (R&S, SP)
harold@cisco.com
México móvil: +52 1 55 8312 4915
Cisco México
Paseo de la Reforma 222
Piso 19
Cuauhtémoc, Juárez
Ciudad de México, 06600
México

Hi,

thanks very much for your input. I am very greatful as I am shor time putting these configs and they should work!

Yes you are correct and I need to fix that jus the same way /21 and /20 prefix is.

Otherwise, the config looks OK to you ?

Regards,

Masood

I have already talked to the provider and they told me that they have advertised that /24 for us. for that reason I used it because /30s from this /24 are used for connectivity between our devices - this is a whole new Infrastructure.

may be after this I get time to take my CCIE R&S written exam.

Thx,

Masood

Masood:

I know youre pressed for time, but can you do me a favor and post the final and corrected configs? This is a pretty good learning scenario and I would like to dissect it.

Making remarks next to each command line to exlain its purpose would be awesome.

Thanks, much appreciated.

you mean the whole router configurations?

as for bGP, this is the whole cofig!? I beleive so?

I will do that as soon as I get this Bad SUP 720 replaced.

I will post a drawing too.

Regards,

Masood

masood:

just the BGP config.

I thought you were going to make a correction to it, as per your post to mohammed. thats why i asked for the revised and final/corrected config.

[edit] The comments on the command lines and a drawing would be awesome!

Thanks

hello again,

one more question?

can I use the CIDER notation in these IP prefix-lists statements?

say, /20 and /19 instead of 255.255.255.240 and .224?

do I need to issue Ip classless command in the routers?

Regards,

Masood

Masood, Im no BGP guru, as you can tell, but I am sure you can use the "/" notation for prefix lists. Also, I believe ip classless is enabled by default these days, and I would say, yes, you should have it enabled.

Im sure Mohammed will be on in a sec to comfirm or deny. :-)

Victor

I am dealing with a very old and used backbone router and I havebeen here just a few days so I had no time to really load the IOS image that I wanted, etc.

I will post the final BGP config this p.m.

as is they work fine. I just need totake out one /19 of the same block, the 240 one out of the first config and put /19 in one and one /20 in the other router.

I will comment the configuration out as it might become useful to the folks on netpro at some point.

Regards,

Masood

hi,

after I added the BGP configuration as listed for border 1, the router added seq numbers to it by itself! as follows:

ip prefix-list default seq 5 permit 0.0.0.0/0

!

ip prefix-list firstblock seq 5 permit 216.x.224.0/20

ip prefix-list firstblock seq 10 permit 216.y.192.0/20

ip prefix-list firstblock seq 15 permit 216.z.224.0/19

!

is this OK?

Please advise.

Regards,

Masood

Masood:

This is perfectly normal.

Sequence numbers allow you to add filter lines to an existing list without having to do it all over again.

It also allows you to delete a line at a time, without having to wipe out the entire list and start over.

If you dont specify the sequence number, the IOS will automatically insert numbers in increments of 5, starting at 5.

This is normal. No worries.

Victor

Thanks Victor. I really got worried. in past I had done it myself but this time, I just didn't add the Seq #s. it seems that I need to go back and study the IOS capability all over again!

I like to keep this post open untit this works if you don'y mind? i will rate this later and gladely.

Thanks much.

Masood

masood, no worries, buddy. I know the feeling.

Let me guess: you're at a client site because you were bum-rushed into a cluster-f%$# situation, and now they want you to fix everything -- immediately! LOL

Glad I could help. Relax, it will go fine. You know what youre doing.

Victor

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