Voting for B,
by deduction:
NOT A - 192.0.2.0/24 is not matched by the route-map, hence it's not advertised
NOT C - only traffic to 192.0.2.0/24 and 192.168.1.0/24 is dropped
NOT D - R1 drops only traffic to 182.0.2.0/24 and 192.168.1.0/24 regardless of LP
B - all traffic to 192.168.1.0/24 is dropped by changing the n-h to 192.0.2.1 (Null0 interface)
The answer is B ,
this is a RTBH topology using R1 as trigger router and R2 as Router exposed to DDOS Attacks, the R1(RTBH) has a full-mesh IBGP sessions with all PE included R2, so R2 when it recieve the prefixe 192.168.1.0/24 witch nexthop 192.0.2.0 , R2 try to loockup to nexthop 192.0.2.0 which is has a nexthop to blackhop null0 , that's why traffic to 192.168.1.0/24 should be dropped .
Obviously B is correct. Because R1 send all packets for 192.168.1.0/24 to Null0 and advertise this route to R2. A is not correct because R1 cant advertise 192.168.2.0/24 (it is not matched by the route-map). C is not correct because there is no configuration to drop all traffic. D is not correct because R1 does not match traffic by local preference
Answer is B, a route to 192.0.2.0/24 is not being advertised. As you see from the example provided, the 'ip route 192.0.2.0 255.255.255.0 null 0' command has been configured on Router 1 & 2.
Hence a route to 192.0.2.0/24 is not being advertised, rather the NEXT_HOP NLRI is being modified and advertised. When this NLRI is advertised via BGP, neighbors will look at their route to 192.168.1.0/24 and modify the NEXT_HOP to go via 192.0.2.1/24 out Null0 with a higher LP so it's preferred over other paths, all traffic to 192.168.1.0/24 will be routed via Nul0 and DROPPED.
LOL I CHANGED MY ANSWER BACK TO A
heres why:
question a states that 192.0.2.0 is being advertised which it is because:
in the route-map ddos
match tag 1
set ip next-hop 192.0.2.1 (here is your network)
then the route-map ddos permit 20 (permits it in the BGP)
lastly
router bgp 65513
redistribue static route-map ddos (this is advertising the next-hop found in the route-map!)
therefore answer A.Router 1 and Router 2 advertise the route to 192.0.2.0 to all BGP peers. is correct!
I think it is a trap question and A is the correct answer. Pay attention to the configuration, in fact, the prefix 192.0.2.0 was not configured with the TAG 1 but the route-map has a second line allowing the rest of the prefixes "permit 20". This prefix will match this line and will be allowed.
My doubt is because R2 is not showing any BGP configuration.
Your understanding is correct, however BGP configuration on R2 are not show. Given the fact that these configurations are for RTBH, B will appear to most correct answer.
I think answer is B, the route map matches Tag 1, which is 192.168.1.0/24 and Not 192.0.2.0/24, so option A does not appear correct.
upvoted 3 times
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