Posted on by patrickmarcpreuss

BGP – MultiHomeing

  1. BGP Prevent becoming an Transit AS
    1. No-Export Community
  2. Cisco
    1. cisco01
      1. config
      2. show ip bgp summary
      3. show ip route
      4. show ip bgp
    2. cisco02
      1. config
      2. show ip bgp summary
      3. show ip route
  3. EdgeRouter-X
    1. edge01
      1. config
      2. show ip route
    2. edge02
      1. config
      2. show ip route
  4. FortiGate
    1. config
    2. get router info routing-table details
  5. Tests
  6. Links

BGP Prevent becoming an Transit AS

The soution at hand is a Filter-list with AS-PATH access-list on the provider bgp session to let only local AS numbers out. Other Solution are 

R1(config)#ip as-path access-list 1 permit ^$
R1(config-router)#neighbor 192.168.12.2 filter-list 1 out

No-Export Community

R1(config)#route-map NO-EXPORT
R1(config-route-map)#set community no-export

R1(config)#router bgp 1
R1(config-router)#neighbor 192.168.12.2 route-map NO-EXPORT in

Cisco

cisco01

config 

ip as-path access-list 1 permit ^$
!
interface Vlan916
 ip address 10.29.1.21 255.255.255.248
!
interface Vlan581
 ip address 10.255.80.28 255.255.255.240
!
router bgp 65021
 bgp log-neighbor-changes
 network 10.255.4.0 mask 255.255.255.0
 network 10.255.80.0 mask 255.255.240.0
 network 10.255.96.0 mask 255.255.240.0
 network 10.255.112.0 mask 255.255.240.0
 neighbor 10.29.1.18 remote-as 65011
 neighbor 10.29.1.18 filter-list 1 out
 neighbor 10.255.80.29 remote-as 65021
 maximum-paths eibgp 4
!

show ip bgp summary

show ip bgp summary
BGP router identifier 10.255.0.1, local AS number 65021
BGP table version is 40, main routing table version 40
7 network entries using 1008 bytes of memory
14 path entries using 1232 bytes of memory
3 multipath network entries and 6 multipath paths
6/3 BGP path/bestpath attribute entries using 1104 bytes of memory
2 BGP AS-PATH entries using 48 bytes of memory
0 BGP route-map cache entries using 0 bytes of memory
0 BGP filter-list cache entries using 0 bytes of memory
BGP using 3392 total bytes of memory
BGP activity 14/7 prefixes, 48/34 paths, scan interval 60 secs
7 networks peaked at 18:09:33 Jun 22 2024 UTC (00:35:00.223 ago)

Neighbor        V           AS MsgRcvd MsgSent   TblVer  InQ OutQ Up/Down  State/PfxRcd
10.29.1.18      4        65011      19      27       40    0    0 00:15:10        3
10.255.80.29    4        65021      56      63       40    0    0 00:37:18        7

show ip route

cisco01#show ip route
Codes: L - local, C - connected, S - static, R - RIP, M - mobile, B - BGP
       D - EIGRP, EX - EIGRP external, O - OSPF, IA - OSPF inter area
       N1 - OSPF NSSA external type 1, N2 - OSPF NSSA external type 2
       E1 - OSPF external type 1, E2 - OSPF external type 2, m - OMP
       n - NAT, Ni - NAT inside, No - NAT outside, Nd - NAT DIA
       i - IS-IS, su - IS-IS summary, L1 - IS-IS level-1, L2 - IS-IS level-2
       ia - IS-IS inter area, * - candidate default, U - per-user static route
       H - NHRP, G - NHRP registered, g - NHRP registration summary
       o - ODR, P - periodic downloaded static route, l - LISP
       a - application route
       + - replicated route, % - next hop override, p - overrides from PfR
       & - replicated local route overrides by connected

Gateway of last resort is 10.255.80.29 to network 0.0.0.0

B*    0.0.0.0/0 [20/0] via 10.255.80.29, 01:17:01
                [20/0] via 10.29.1.18, 01:17:01

show ip bgp

show ip bgp
BGP table version is 40, local router ID is 10.255.0.1
Status codes: s suppressed, d damped, h history, * valid, > best, i - internal,
              r RIB-failure, S Stale, m multipath, b backup-path, f RT-Filter,
              x best-external, a additional-path, c RIB-compressed,
              t secondary path, L long-lived-stale,
Origin codes: i - IGP, e - EGP, ? - incomplete
RPKI validation codes: V valid, I invalid, N Not found

     Network          Next Hop            Metric LocPrf Weight Path
 *mi  0.0.0.0          10.255.80.29             0    100      0 65011 65001 i
 *>                    10.29.1.18                             0 65011 65001 i

cisco02

config 

ip as-path access-list 1 permit ^$
!
interface Vlan581
 ip address 10.255.80.29 255.255.255.240
!
interface Vlan917
 ip address 10.29.1.5 255.255.255.248
!
router bgp 65021
 bgp log-neighbor-changes
 network 10.255.4.0 mask 255.255.255.0
 network 10.255.80.0 mask 255.255.240.0
 network 10.255.96.0 mask 255.255.240.0
 network 10.255.112.0 mask 255.255.240.0
 neighbor 10.29.1.3 remote-as 65011
 neighbor 10.29.1.3 filter-list 1 out
 neighbor 10.255.80.28 remote-as 65021
 maximum-paths eibgp 4
!

show ip bgp summary

show ip bgp summary
BGP router identifier 10.255.0.2, local AS number 65021
BGP table version is 25, main routing table version 25
7 network entries using 1008 bytes of memory
14 path entries using 1232 bytes of memory
3 multipath network entries and 6 multipath paths
6/3 BGP path/bestpath attribute entries using 1104 bytes of memory
2 BGP AS-PATH entries using 48 bytes of memory
0 BGP route-map cache entries using 0 bytes of memory
0 BGP filter-list cache entries using 0 bytes of memory
BGP using 3392 total bytes of memory
BGP activity 14/7 prefixes, 40/26 paths, scan interval 60 secs
7 networks peaked at 18:09:33 Jun 22 2024 UTC (00:38:23.699 ago)

Neighbor        V           AS MsgRcvd MsgSent   TblVer  InQ OutQ Up/Down  State/PfxRcd
10.29.1.3       4        65011      46      55       25    0    0 00:40:43        3
10.255.80.28    4        65021      67      60       25    0    0 00:40:41        7

show ip route

cisco02#show ip route
Codes: L - local, C - connected, S - static, R - RIP, M - mobile, B - BGP
       D - EIGRP, EX - EIGRP external, O - OSPF, IA - OSPF inter area
       N1 - OSPF NSSA external type 1, N2 - OSPF NSSA external type 2
       E1 - OSPF external type 1, E2 - OSPF external type 2, m - OMP
       n - NAT, Ni - NAT inside, No - NAT outside, Nd - NAT DIA
       i - IS-IS, su - IS-IS summary, L1 - IS-IS level-1, L2 - IS-IS level-2
       ia - IS-IS inter area, * - candidate default, U - per-user static route
       H - NHRP, G - NHRP registered, g - NHRP registration summary
       o - ODR, P - periodic downloaded static route, l - LISP
       a - application route
       + - replicated route, % - next hop override, p - overrides from PfR
       & - replicated local route overrides by connected

Gateway of last resort is 10.255.80.28 to network 0.0.0.0

B*    0.0.0.0/0 [20/0] via 10.255.80.28, 01:17:49
                [20/0] via 10.29.1.3, 01:17:49

EdgeRouter-X

edge01

config

set interfaces ethernet eth0 vif 916 address 10.29.1.18/29
set interfaces ethernet eth0 vif 997 address 10.255.2.8/28
set interfaces ethernet eth3 address 10.29.1.9/29
set interfaces loopback lo address 10.29.0.1/32

set protocols bgp 65011 neighbor 10.29.1.14 remote-as 65011
set protocols bgp 65011 neighbor 10.29.1.21 remote-as 65021
set protocols bgp 65011 neighbor 10.255.2.5 local-as 65111
set protocols bgp 65011 neighbor 10.255.2.5 remote-as 65001
set protocols bgp 65011 network 10.29.0.1/32
set protocols bgp 65011 parameters log-neighbor-changes
set protocols bgp 65011 parameters router-id 10.29.0.1

show ip route

ubnt01:~$ show ip route
Codes: K - kernel, C - connected, S - static, R - RIP, B - BGP
       O - OSPF, IA - OSPF inter area
       N1 - OSPF NSSA external type 1, N2 - OSPF NSSA external type 2
       E1 - OSPF external type 1, E2 - OSPF external type 2
       > - selected route, * - FIB route, p - stale info

IP Route Table for VRF "default"
B    *> 0.0.0.0/0 [200/0] via 10.255.2.5, eth0.997, 01:05:15
B    *> 10.29.0.2/32 [200/0] via 10.29.1.14, eth3, 01:15:12
B    *> 10.255.4.0/24 [20/0] via 10.29.1.21, eth0.916, 01:05:19

edge02

config

set interfaces ethernet eth0 address 10.29.1.3/29
set interfaces ethernet eth0 vif 997 address 10.255.2.9/28
set interfaces ethernet eth3 address 10.29.1.14/29
set interfaces loopback lo address 10.29.0.2/32

set protocols bgp 65011 neighbor 10.29.1.5 remote-as 65021
set protocols bgp 65011 neighbor 10.29.1.9 description de052-ne1-rt-ubnt01
set protocols bgp 65011 neighbor 10.29.1.9 remote-as 65011
set protocols bgp 65011 neighbor 10.255.2.5 remote-as 65001
set protocols bgp 65011 network 10.29.0.2/32
set protocols bgp 65011 parameters log-neighbor-changes
set protocols bgp 65011 parameters router-id 10.29.0.2

show ip route

ubnt02:~$ show ip route
Codes: K - kernel, C - connected, S - static, R - RIP, B - BGP
       O - OSPF, IA - OSPF inter area
       N1 - OSPF NSSA external type 1, N2 - OSPF NSSA external type 2
       E1 - OSPF external type 1, E2 - OSPF external type 2
       > - selected route, * - FIB route, p - stale info

IP Route Table for VRF "default"
B    *> 0.0.0.0/0 [20/0] via 10.255.2.5, eth0.997, 35w5d06h
B    *> 10.29.0.1/32 [200/0] via 10.29.1.9, eth3, 01:06:30
B    *> 10.255.4.0/24 [20/0] via 10.29.1.5, eth0, 35w5d06h

FortiGate

config

config system interface
    edit "port1.997"
        set vdom "root"
        set ip 10.255.2.5 255.255.255.240
        set interface "port1"
        set vlanid 997
    next
end
config router bgp
    set as 65001
    set router-id 10.255.2.5
    set ebgp-multipath enable
    config neighbor
        edit "10.255.2.9"
            set activate6 disable
            set activate-vpnv4 disable
            set capability-default-originate enable
            set remote-as 65011
        next
        edit "10.255.2.8"
            set activate6 disable
            set activate-vpnv4 disable
            set capability-default-originate enable
            set remote-as 65011
        next
    end
   
end

get router info routing-table details

forti01 # get router info routing-table details
Codes: K - kernel, C - connected, S - static, R - RIP, B - BGP
       O - OSPF, IA - OSPF inter area
       N1 - OSPF NSSA external type 1, N2 - OSPF NSSA external type 2
       E1 - OSPF external type 1, E2 - OSPF external type 2
       i - IS-IS, L1 - IS-IS level-1, L2 - IS-IS level-2, ia - IS-IS inter area
       V - BGP VPNv4
       * - candidate default

Routing table for VRF=0
S*      0.0.0.0/0 [1/0] via 62.155.244.225, ppp2, [1/0]

Tests

traceroute -n  8.8.8.8
traceroute to 8.8.8.8 (8.8.8.8), 30 hops max, 60 byte packets
 1  10.255.4.2  1.380 ms  1.345 ms  1.345 ms
 2  10.255.80.29  1.136 ms 10.29.1.18  0.616 ms 10.255.80.29  1.079 ms
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