Task 5

FYI, the question is truncated….

1. r2 should aggregate all the networks in 3.1.0.0 address space………..
2. Aggregation should be configured such that R1 in AS 100 is the only AS that receives the aggregate route, R3 and future peer neighbors should NOT receive the aggregate route.
3. R1 should not use R3 if network 3.1.11.0/24 is down

1. r2 should aggregate all the networks in 3.1.0.0 address space………..

R1(config-if)#do sho ip bgp
BGP table version is 6, local router ID is 10.1.12.1
Status codes: s suppressed, d damped, h history, * valid, > best, i – internal,
r RIB-failure, S Stale
Origin codes: i – IGP, e – EGP, ? – incomplete

Network          Next Hop            Metric LocPrf Weight Path
*> 2.2.2.0/24       10.1.12.2                0             0 200 i
*> 3.1.0.0/20       10.1.12.2                0             0 200 300 i
*> 3.1.11.0/24      0.0.0.0                  0         32768 i

TASK 7 & 9

If net 2.0.0.0 is up and it’s advertised to R1, R1 should take the

actions:
-R1 should advertise network 1.0.0.0/8 to R3
-R1 should remove network 2.0.0.0/8 from it’s BGP table.

to conditionally advertise we can use the following

commands:
advertise-map
non-exist-map
exist-map.

r1
access-list 1 permit 1.0.0.0 0.255.255.255
access-list 2 permit 2.0.0.0 0.255.255.255
route-map ADV per 10
match ip add 1
route-map NotThere per 10
match ip add 2

router bgp 100
neighbor 10.1.13.3 advertise-map ADV non-exist-map NotThere

advertise-map map-name
Specifies the name of the route map that will be advertised if the conditions of the exist map or nonexist map are met.

exist-map map-name
Specifies the name of the route map that will be compared to the advertise map. If the condition is met and a match occurs between the advertise map and exist map, the route will be advertised. If no match occurs, then the condition is not met, and the route iswithdrawn.

non-exist-map map-name
Specifies the name of the route map that will be compared to the advertise map. If the condition is met and no match occurs, the route will be advertised. If a match occurs, then the condition is not met, and the route is withdrawn.

note: the advertise-map specifies the name of the route-map that will be advertised if the condition of the non-exsit-map is met.

neighbor 10.1.13.3 advertise-map ADV(match 1.0.0.0) non-exist-map

NotThere (match 2.0.0.0)

so bgp will advertise 1.0.0.0 if 2.0.0.0 is not there. But if the 2.0.0.0 is there then it will not advertise the 1.0.0.0 prefix.

note: the non-exist-map specifies the route-map that will be compared to the advertise-map. If the condition is met then the route will be advertised. If a match occurs then the condition is NOT met and the route will be withdrawn.

neighbor 10.1.13.3 advertise-map ADV(match 1.0.0.0) non-exist-map

NotThere (match 2.0.0.0)

so because 2.0.0.0 is there when the non-exist-map looks to match the

2.0.0.0 prefix then the 1.0.0.0 prefix is not advertised

sho ip bgp nei 10.1.13.3 advertised-routes

————————————————————-

1- if both 1.0.0.0 & 2.0.0.0 are up then both networks should be

advertised to R3.
2-if net 1.0.0.0 is down, R1 should NOT advertise net 2.0.0.0 to R3
3-if net 2.0.0.0 is down, then R1 should only advertise 1.0.0.0 to R3

access-list 1 per 1.0.0.0 0.255.255.255
access-list 2 per 2.0.0.0 0.255.255.255

route-map ADV per 10
match ip add 2.0.0.0
route-map EXIST per 10
match ip add 1.0.0.0

router bgp 100
neig 10.1.13.3 advertise-map ADV (2.0.0.0) exist-map EXIST (1.0.0.0)

so if the exist-map matches the prefix’s in EXIST (1.0.0.0) and in the advertise-map ADV (2.0.0.0) then the prefix is advertised.

to test condition #1
sh ip bgp nei 10.1.13.3 advertised-routes

BGP table version is 20, local router ID is 1.1.1.1
Status codes: s suppressed, d damped, h history, * valid, > best, i -

internal,
r RIB-failure, S Stale
Origin codes: i – IGP, e – EGP, ? – incomplete

Network          Next Hop            Metric LocPrf Weight Path
*> 1.0.0.0          0.0.0.0                  0         32768 i
*> 2.0.0.0          10.1.12.2                0             0 200 i

note: since EXIST and ADV both match the prefix’s in the bgp table both networks are advertised. So since 1.0.0.0 exists both 1.0.0.0

and 2.0.0.0 will be advertised. to test conditon #2 – so if 1.0.0.0 is down it should not advertise 2.0.0.0

r1
int lo0
shut

sh ip bgp nei 10.1.13.3 advertised-routes
Total number of prefixes 0

note:since the exist-map did not match EXIST (because 1.0.0.0 is down and hte prefix is not in the bgp table) the EXIST prefix and ADV prefix is not advertised.

to test condition #3 – if 2.0.0.0 is down it should advertise 1.0.0.0
sho ip bgp nei 10.1.13.3 adver
BGP table version is 21, local router ID is 1.1.1.1
Status codes: s suppressed, d damped, h history, * valid, > best, i -

internal,
r RIB-failure, S Stale
Origin codes: i – IGP, e – EGP, ? – incomplete

Network          Next Hop            Metric LocPrf Weight Path
*> 1.0.0.0          0.0.0.0                  0         32768 i

Total number of prefixes 1

note: since the advertise-map (2.0.0.0 is down) did not match ADV 2.0.0.0 was not advertised.

————————————————

neig 10.1.13.3 advertise-map ADV (2.0.0.0) exist-map EXIST (1.0.0.0)

if 1.0.0.0 prefix esists advertsise both 1.0.0.0 & 2.0.0.0.
if 1.0.0.0 does not exist do not advertise anything.
if 1.0.0.0 exists but 2.0.0.0 does not exist advertise 1.0.0.0.

neighbor 10.1.13.3 advertise-map ADV(match 1.0.0.0) non-exist-map

NotThere (match 2.0.0.0)

if 2.0.0.0 does not exist advertise 1.0.0.0
if 2.0.0.0 does exist 2.0.0.0 will be advertised and ADV 1.0.0.0

will not be advertised. The point of a non-exist-map is that there should be no match and if there is a match then the advertise-map is not advertised even if the prefix is in the bgp table. so bgp will advertise 1.0.0.0 if 2.0.0.0 is not there. But if the 2.0.0.0 is there then it will not advertise the 1.0.0.0 prefix

clear ip bgp *  for the changes to take effect.

This is pretty easy if you don’t get confused  by the question. Using route-map names that make sense also help tremendously

Completed Narbik’s advanced wb BGP lab 2 – route reflectors.

Today I read Sam Halabi’s BGP4 Case Studies/Tutorial. I really enjoyed reading this 100 page document.  Sam provided a good example for each topic.

Some things  to remember:

BGP back door – manipultes  the IGP admin distance to prefer the IGP vs EBGP.

BGP load balancing = 1. loopbacks 2. maximum path command

as-set – append  to prevent advertising the atomic aggregate. This forces the router to generatepath information in the form of a set {}.

weight = local to the router – set on updates coming into the router – higher is preferred

routerc

or

routerc

local-preference - local to the AS – set on updates out of the router – higher is preferred

eg..

MED – a hint to external neighbors about the preferred path into a network – exchanged between AS’s – lower is preferred – BGP ALWAYS-COMPARE-MED is needed for a router to compare MED’s from a DIFFERENT AS.

eg..

BGP path manipulation

BGP path manipulation

Why laugh at me?