BGP Multi Homing

[alshamlan]

Dear,

I am an ISP that have multi homing with two upsteam provider. I have BGP configuration with both ISP.

ISP - A : send me full routing BGP table and it worked with me fine when the ISP-B disconnected ( for outgoing and incoming traffic)

ISP-B : send me the defualt route 0.0.0.0 only,

when both are connected the outgoing always from ISP-A and incoming from ISP-B. however, whenever i disconnect ISP-A I cannot receive or send any traffic through ISP-B .

apprciate your help and cooperation.

regards

MHS

[Azhar Munawar]

you can do one more thing define static route for google with destination isp b then run traceroute command to see where its stuck its simple to identify.

Regards,

Azhar

[alshamlan]

you mean to do the below

ip route  google_ip  255.255.255.255   IP_address_ISP-B ?

regards

MHS

[Azhar Munawar]

yes and then run trace route.

Regards,

Azhar

[alshamlan]

I tried it.

No response from any hop at all it is not going out from my router.

any advice.

regards

MHS

[Azhar Munawar]

Means there is problem with your router configuration you have to check your configuration.

If you are online PM me then we can resolve it now.

Regards,

Azhar

[germain85]

Hi Azhar, Alshamlan

It's very interessant. Just a few question to Alshamlan, are you able to ping your ISP_B network when ISP_A is shut? Not from your Edge router.

Reagards,

Germain,

[alshamlan]

Hi Germain,

No I cannot ping ISP_B from my network when ISP-A down. however, the looking glass shows clearly that the incoming traffic is through ISP-B when ISP-A up. but, no incoming or outgoing with ISP-B when ISP-A down.

Azhar, Tell me when you be avaiable.

Is there any problem if the point to point IP addresses between me and ISP-B is from my network sunbet.

regrads

MHS

[Azhar Munawar]

Dear MHS,

I am available tell me your suitable time.

First we have to check the simple trace results with your BGP IP with ISP B , BGP is second routes are second thing thing.

Did you define static route for google.com with destination address of isp B default address?

If its possible for you kindly share with me your bgp and routes output you can change your IPs and AS with other address for safety,

Regards,

Azhar

[alshamlan]

Hi Azhar,

MY show ip bgp out put is

   Network          Next Hop            Metric LocPrf Weight Path

*> 0.0.0.0          ISP-B interface                           0 ISP-B i

after this route there is BGP routes from ISP-A

Show ip route is

B*    0.0.0.0/0 [20/0] via ISP-B interfecae , 00:46:24

after that the BGP route to ISP-A

      1.0.0.0/8 is variably subnetted, 839 subnets, 14 masks

How  I can force my traffic to go through ISP-B, I used to shut ISP-A to do  it but still as I inform you it didnt work once I shut down ISP-A

regards

MHS

[Azhar Munawar]

Dear MHS,

You dont need to shutdown ISP A interface just define this route

ip route static google(IP) 255.255.255.255 ISP B interfaceIP

when you ping google ip its choose isp B interface for exit your router.

you can chech this with this command

show cef exact-router source IP and destination ip (google ip)

it shows you the interface choosed for exit interface.

Regards,

Azhar

[alshamlan]

Hi Azhar,

I did the static route and it showed me that the exist interface is ISP-B.

Router#show ip cef exact-route Source-IP 209.85.229.99

Source-IP -> 209.85.229.99 => IP adj out of ISP-B ineterface, addr ISP-B interface

regards

MHS

[argnetworking]

Can you send a basic diagram of your topology?

When you shutdown ISPA, does your router knows how to get to your ISPB router?

Remember that BGP check first if it can get to the next hop and then install the route in the routing table.

Regards,

Gonzalo

[Azhar Munawar]

Dear MHS,

Sorry exact command sh ip cef exact-route source ip destination ip.

for example

sh ip cef exact-route 1.1.1.1 2.2.2.2

it will show you the route path.

I sent you PM kindly check it.

Regards,

Azhar

[alshamlan]

Hi Azhar,

I did the static route and it showed me that the exist interface is ISP-B.

Router#show ip cef exact-route Source-IP 209.85.229.99

Source-IP -> 209.85.229.99 => IP adj out of ISP-B ineterface, addr ISP-B interface

regards

MHS

[alshamlan]

ISP-A sending full BGP routing to me, and I am sending the full subnet with half subnet.

ISP-B sending to me the defualt route and I am sending the full subnet and the other half of the subnet.