Symptoms
It's been a long standing ask for XR to support conditional route advertisements in BGP.
The expected option of using the
if rib-has-route
option in RPL currently can only be used at the default-information originate attachpoint to conditionally advertise a default route out.
The actual request is documented under
CSCue04899 Allow 'rib-has-route' for outbound rpl
there are some reasonable technical limitations as to why it has not happened yet, but there is a neat workaround that I would like to share that provides the exact same behavior!
Components involved
The logic of the workaround solution is as follows:
- In BGP one defines a network statement for the route that needs to be conditionally advertised. (One could possible instead of a network statement also use redistribute static with a route-policy using a prefix-set)
- This network statement's prefix is defined as a static route under router static
- The static route references the outgoing interface Null0 and a object track definition
- The object track definition references something that you want to track.
The tracking options include:
bfdrtr track type bfd rtr
line-protocol track type line-protocol; the line protocol of an interface, this interface can be l2transport or an l3 interface of any kind
list track type list; this allows you to track other track definitions in an AND or OR manner
route track type ipv4 route ; the presence of a route
rtr track type ipsla; an IPSLA probe to verify an end to end connectivity or port or anything that IPSLA can monitor!
Detailed Solution
This example talks you through a solution of using the BGP network statement, a conditional static route and the dependency on an interface line state
Config pieces:
Static route that is conditional with a tracker called MYIF
router static
address-family ipv4 unicast
192.168.123.0/24 Null0 track MYIF
Tracker MYIF that checks a lineprotocol state:
track MYIF
type line-protocol state
interface TenGigE0/2/0/3
BGP configuration that advertises a prefix (that is now conditional)
router bgp 64524
address-family ipv4 unicast
network 192.168.123.0/24
Sample operation:
Tracking interface is DOWN:
LC/0/2/CPU0:Jun 12 09:41:33 : ifmgr[210]: %PKT_INFRA-LINK-3-UPDOWN : Interface TenGigE0/2/0/3, changed state to Down
LC/0/2/CPU0:Jun 12 09:41:33 : ifmgr[210]: %PKT_INFRA-LINEPROTO-5-UPDOWN : Line protocol on Interface TenGigE0/2/0/3, changed state to Dn
Verify the static route is not there:
RP/0/RSP0/CPU0:A9K-BNG(config-if)#do sh route static | i 192.168.123
Wed Jun 12 09:41:18.977 EDT
RP/0/RSP0/CPU0:A9K-BNG(config-if)#
Now bring up the interface, in this case it is not connected so i force it up with a loopback
RP/0/RSP0/CPU0:A9K-BNG(config-if)#loop int
RP/0/RSP0/CPU0:A9K-BNG(config-if)#commit
Wed Jun 12 09:41:33.044 EDT
LC/0/2/CPU0:Jun 12 09:41:33 : ifmgr[210]: %PKT_INFRA-LINK-3-UPDOWN : Interface TenGigE0/2/0/3, changed state to Up
LC/0/2/CPU0:Jun 12 09:41:33 : ifmgr[210]: %PKT_INFRA-LINEPROTO-5-UPDOWN : Line protocol on Interface TenGigE0/2/0/3, changed state to Up
Notice the tracker detects it and ups the object!
RP/0/RSP0/CPU0:Jun 12 09:41:33 : object_tracking[359]: %SERVICES-OT-6-TRACK_INFO : track MYIF state Track_Up
Verify the static route again:
RP/0/RSP0/CPU0:A9K-BNG(config-if)#do sh route static | i 192.168.123
Wed Jun 12 09:41:58.463 EDT
S 192.168.123.0/24 is directly connected, 00:00:24, Null0
Interface that is tracked configuration. Note that you can also track l2transport interfaces!!
interface TenGigE0/2/0/3
description InternalLoop-trackertest
loopback internal
l2transport
!
cheers!
xander
=====
Xander Thuijs, CCIE #6775
Distinguished Engineer ASR9000/NCS5500/IOS-XR
