EBGP Example: Martian Routes

adeel32

Dear All,

During EBGP example on page 512 of JNCIP book, i have not fully understood the points

• No customer routes that donot originate in that customer's AS
• No 0-127 routes with prefix lengths less than /8

Can anyone able to breifly explain and solve the points?

Regards
Adeel Ahmed

hoogen82

Customer routes are originated from the AS 65010 or 65020.. So for eg R4 peering with C1.. it should make sure that the routes it received from C1 are originated there... and not from some other AS... usually with a regex which says ".* 65010".. where 65010 is the orignated AS.. routes can pass through other AS but is originated from 65010..

0-127 is pretty straightforward.. 0/1 prefix-length-range /1-/7... They say less than /8.. so you keep it till /7...

adeel32

Thanks for your reply

Robert_74

Hi Guys,

just for the sake of discussion - would not it be more correct to use something like (65010|65020) for the routes "that do not originate in that customer's AS" instead of .*65010(or 20)

What is the assumption of having other AS numbers in the path from dirrectly connected AS ??


I am not quite sure here, but this example it
very close to cisco "equivalnent" directly connected AS.
Firstly this as-path only applied to C1/2 routers, meaning that the customer routesd are expected only from directly connected AS.
If we take .*65010 as for eg path "1 2 4 7 89 65010" it will still be allowed,
and in theory correct, but from customer rospective this path is looped so would never happen.
What is the assumption of having other AS numbers in the path from dirrectly connected AS ??

Thanks
Robert

hoogen82

Your assumption is correct... I haven't found out the answer myself. The only thing I found out was when I was building up the lab, the configurations of C1 and C2 seem to have routes with as numbers prepended..something like

route 32.0.0.0/16 {
discard;
as-path {
path 420;
}

In which 420 as path is added onto a route. So my theory of going with the *65010... There are some questions even when you take the CCIE.. you just have to ask the proctor to be sure... I guess this is one such question.. ask the proctor... The question is still valid..

Robert_74

Thanks Hoogen82, nice to know that I am not the only one asking this question. Looks like the Proctor is going to be the last resort for this matter