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iBGP firewall transversal

I have 2 routers outside a firewall and one router inside the firewall (Checkpoint). I need to set up an iBGP mesh between all 3. Is there any "gotcha" I should consider when setting this up?

Thanks,

Hank

2 REPLIES
Purple

Re: iBGP firewall transversal

Hi Hank,

I can't imagine that there would be too many issues since BGP is carried over TCP. If you are doing some form of NAT on the firewall, you will have to be mindful that the BGP payload will not be translated...

Paresh

Cisco Employee

Re: iBGP firewall transversal

One thing to be careful about if you are using MD5 authentication. Most firewalls including Checkpoint will change the initial sequence number received from TCP peers. While this is perfectly ok generally, this will not work if you use MD5 authentication as the TCP sequence number is part of the information included in the MD5 hash inserted in the TCP header and modifying it will cause the TCP segment to be discarded.

For MD5 to work through the FW, Initial sequence number randomization needs to be disable at least for this session. On the PIX you would use the following command to do that:

static (inside,outside) netmask 0 0 norandomseq

I'm not sure though how you accomplish the same thing on the Checkpoint FW.

Hope this helps,

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
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