Category: Route

Similarities to IPv4

• Redistribution takes routes from the IP routing table, not from the iGP databases.
• Route maps can be used for filtering, metrics, route tags.
• Admnistrative distance has not changed.
• Options to prevent routing loops; Administrative distance, route tags, filtering.
• Syntax is the same.

Differences to IPv4

• Supported “match” commands in route-maps vary on iGP
  • OSPF/RIP cannot match op “route-type” with a Route-map
    • EIGRP has no problems using “route-type”
  • Route-map matching IPv6 ACLs must have IPv6 prefix as source portion and “any” as destination of ACL.
• IPv6 redistribute connected does not include interfaces running the iGP;
  • redistribute include-connected

RIPng

• UPD port number 521
• No autosummarization for IPv6
• Destination address FF02::9
• Link-Local next-hops
• IPv6 uses IPv6 AH/ESP Authentication
• Enable it on the interface
  • ipv6 rip CCNP enable fa0/0
• No network command

EIGRP IPv6

• EIGRP uses the neighbor’s link local address as the next-hop
• Destination FF02::AA
• Authentication relies on the IPv6 built-in authentication nad privacy
• IPv4 defaults to auto summarization, IPv6 doesn’t
  • ipv6 unicast-routing
  • ipv6 route eigrp 100
  • (config-if)#ipv6 eigrp 100
  • eigrp router-id RID

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BGP Path Attributes

“We Love Oranges AS Oranges Mean Pure Refreshment”

R1#sh ip bgp 40.40.40.0
*Mar  1 00:17:21.323: %SYS-5-CONFIG_I: Configured from console by console
R1#sh ip bgp 40.40.40.0
BGP routing table entry for 40.40.40.0/24, version 4
Paths: (2 available, best #1, table Default-IP-Routing-Table)
  Advertised to update-groups:
     1
  30
    3.3.3.2 from 3.3.3.2 (3.3.3.2)
      Origin IGP, metric 0, localpref 100, valid, external, best
  20
    2.2.2.2 from 2.2.2.2 (20.20.20.1)
      Origin IGP, metric 0, localpref 100, valid, external

R1#sh ip bgp
BGP table version is 4, local router ID is 3.3.3.1
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
*> 20.20.20.0/24    2.2.2.2                  0             0 20 i
*> 30.30.30.0/24    3.3.3.2                  0             0 30 i
*> 40.40.40.0/24    3.3.3.2                  0             0 30 i
*                   2.2.2.2                  0             0 20 i

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• BGP filtering can be done on any routers
• Filtering can be done inbound and outbound
• After filtering is applied BGP neighbor must be reset or cleared for the filter to take effect
  • clear ip bgp 20.20.20.20 in/out  preferred
  • clear ip bgp *   (hard reset)
  • clear ip bgp 20.20.20.20 soft in/out

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sh ip bgp

R1#sh ip bgp
BGP table version is 6, local router ID is 10.10.10.1
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,
Origin codes: i - IGP, e - EGP, ? - incomplete
RPKI validation codes: V valid, I invalid, N Not found

     Network          Next Hop            Metric LocPrf Weight Path
     0.0.0.0          0.0.0.0                                0 i
 r>  1.1.1.0/30       20.20.20.1               0             0 20 ?
 r>  20.20.20.0/24    20.20.20.1               0             0 20 ?
 *>  30.30.30.0/24    20.20.20.1               0             0 20 ?
 *>i 40.40.40.0/24    1.1.2.2                  0    100      0 i

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Injecting routes into BGP.

• Use the network command.
  • Different than the network command in iGP; it isn’t used to listen/active interfaces.
  • the BGP network command looks for the prefix in the routing table and originates that into the BGP table.
  • If no mask is defined, IOS assumes a classful network.
  • Classful route is added if:
    • the exact route is in the ip routing table
    • Any subset of routes are in the routing table (only with auto-summery)
  • create a null0 route
    •  ip route 30.30.30.0 255.255.255.0 null0

router bgp 20
 bgp log-neighbor-changes
 network 30.30.30.0 mask 255.255.255.0
 neighbor 10.10.10.1 remote-as 10
 neighbor 10.10.10.1 ebgp-multihop 255
 neighbor 10.10.10.1 update-source Loopback1

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• Multiple path attributes to determine the best path for a certain prefix.
• When no path attributes are set, BGP uses the AS_PATH to determine the best route.
  • Shortest AS path wins
• AS_SEQ is the component of the AS_PATH attribute.
  • 10.10.10.0/24 20 10
    • AS-SEQ (in order)
• With summarization:
  • 10.10.0.0/16 20 10 { 1 2 5 4 3 }  
  • Prefix AS-PATH AS-SEQ  { AS-SET } 
    • AS-SET are not in order
• Prevents Routing loops.
• If a BGP router received an update with it’s own AS#, it indicates a loop.
• If a BGP router received an update with it’s own AS#, it drops the route.

BGP message types

New relation between two BGP peers:

• Open
  • type 1
  • Version4 (ipv4), AS#, Hold time, Router-iD, parameters.

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• idle:
  • BGP is down or waiting next retry
• Connect:
  • The BGP is waiting for the TCP connection to be completed
• Active:
  • The TCP Connection failed, Connect-retry timer running, listening for incoming TCP Connections
• Opensent:
  • The TCP connection exists and a BGP Open Message as been send.
  • The matching Open Message has not yet been received
• Openconfirm:
  • Open Message has been send and received
• Established:
  • All neighbor parameters match
  • Relationship works
  • Peers can exchange update messages

• Local router find the outgoing interface for the neighbor
• the IP of the outgoing interface is used as the source IP by default.
• With one link a failure in that link can lose the neighborship.
  •  configure two neighbor commands
  • Use the loopback interfaces as TCP endpoints
• Loopback links between two AS might miss the route to the peer’s loopback
  • fixed with multihop (TTL=255 instead of TTL=1).
    
    • create routes between peers to reach loopback address.
    • configure update-source so the right source-ip is used.

R10#(config)router bgp 10
R10#(config-router)neighbor 20.20.20.20 remote-as 20
R10#(config-router)neighbor 20.20.20.20 ebgp-multihop
R10#(config-router)neighbor 20.20.20.20 update-source loopback0

R20#(config)router bgp 20
R20#(config-router)neighbor 10.10.10.10 remote-as 10
R20#(config-router)neighbor 10.10.10.10 ebgp-multihop
R20#(config-router)neighbor 10.10.10.10 update-source loopback0