Task 5.6

I will admit I am not an expert by far on BGP but I am questioning this task and I guess I am probably wrong to question it and I'm probably reading too much into things but please let me know if I am or not.

OK, we have AS100 on R1, R3 & R6 with R6 propagating a BGP community attribute to R1 and R3 in order to prevent this AS100 becoming a transit path for the rest of the network (this was all done back in task 5.2).

When we come to this task, we are playing with some more BGP devices in AS100 (SW3 & SW4). In this task 5.6 we want to allow SW3 and SW4 to recieve routes coming in from R1, R3 and R6 which are also in AS100 by using the "allow-as" feature. This concept to me is easy to understand and makes total sense.

My problem is this; in the SG I can see that once this allow-as feature is added, SW3 is suddenly recieving routes with AS54 in the AS Path even though we have denied these routes from propagating to the network in task 5.2 with the community attribute no-export!!!

When I labbed this up I did not get these AS54 routes on SW3 and I hope this is just an error in the SG. Please could someone kindly shed some light on this issue. Many thanks.


  • In my opinion, it's a small mistake. I think they did the solution before they did task 5.2 with filtering based on communities. But you are right, SW3 and SW4 should not see AS 54 routes. 


  • Small mistake?!

    So am correct in saying that this task is totally impossible since the community filtering is applied in task 5.2?

    I would like to learn something from this task, but I cant seem to understand what they were trying to do! :)

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