Operation on a BGP IPv4 LSP resolved over an SR-ISIS IPv4 tunnel, SR-OSPF IPv4 tunnel, or SR-TE IPv4 LSP

SR OS enhances lsp-ping and lsp-trace of a BGP IPv4 LSP resolved over an SR-ISIS IPv4 tunnel, an SR-OSPF IPv4 tunnel, or an SR-TE IPv4 LSP. The SR OS enhancement reports the full set of ECMP next-hops for the transport tunnel at both ingress PE and at the ABR or ASBR. The list of downstream next-hops is reported in the DSMAP or DDMAP TLV.

When the user initiates an lsp-trace of the BGP IPv4 LSP with the path-destination option specified, the CPM hash code, at the responder node, selects the outgoing interface to be returned in DSMAP or DDMAP. This decision is based on the modulo operation of the hash value on the label stack or the IP headers (where the DST IP is replaced by the specific 127/8 prefix address in the multipath type 8 field of the DSMAP or DDMAP) of the echo request message and the number of outgoing interfaces in the ECMP set.

Figure: Example topology for BGP over SR-OSPF, SR-TE (OSPF), SR-ISIS, and SR-TE (ISIS) depicts an example topology used in the subsequent BGP over SR-OSPF, BGP over SR-TE (OSPF), BGP over SR-ISIS, and BGP over SR-TE (ISIS) examples.

Figure: Example topology for BGP over SR-OSPF, SR-TE (OSPF), SR-ISIS, and SR-TE (ISIS)

The following are example outputs of the lsp-trace command for a hierarchical tunnel consisting of a BGP IPv4 LSP resolved over an SR-ISIS IPv4 tunnel, an SR-OSPF IPv4 tunnel, or an SR-TE IPv4 LSP.

BGP over SR-OSPF example output:

*A:Dut-A# oam lsp-trace bgp-label prefix 11.21.1.6/32 detail downstream-map-tlv ddmap path-destination 127.1.1. 
lsp-trace to 11.21.1.6/32: 0 hops min, 0 hops max, 168 byte packets
1  10.20.1.3  rtt=2.31ms rc=8(DSRtrMatchLabel) rsc=2 
     DS 1: ipaddr=10.10.5.5 ifaddr=10.10.5.5 iftype=ipv4Numbered MRU=1496 
           label[1]=27506 protocol=5(OSPF)
           label[2]=262137 protocol=2(BGP)
     DS 2: ipaddr=10.10.11.4 ifaddr=10.10.11.4 iftype=ipv4Numbered MRU=1496 
           label[1]=27406 protocol=5(OSPF)
           label[2]=262137 protocol=2(BGP)
     DS 3: ipaddr=10.10.11.5 ifaddr=10.10.11.5 iftype=ipv4Numbered MRU=1496 
           label[1]=27506 protocol=5(OSPF)
           label[2]=262137 protocol=2(BGP)
2   10.20.1.4  rtt=4.91ms rc=8(DSRtrMatchLabel) rsc=2 
     DS 1: ipaddr=10.10.9.6 ifaddr=10.10.9.6 iftype=ipv4Numbered MRU=1492 
           label[1]=27606 protocol=5(OSPF)
           label[2]=262137 protocol=2(BGP)
3  10.20.1.6  rtt=4.73ms rc=3(EgressRtr) rsc=2 
3  10.20.1.6  rtt=5.44ms rc=3(EgressRtr) rsc=1 
*A:Dut-A#

BGP over SR-TE (OSPF) example output:

*A:Dut-A# oam lsp-trace bgp-label prefix 11.21.1.6/32 detail downstream-map-tlv ddmap path-destination 127.1.1.1 
lsp-trace to 11.21.1.6/32: 0 hops min, 0 hops max, 236 byte packets
1  10.20.1.2  rtt=2.13ms rc=3(EgressRtr) rsc=4 
1  10.20.1.2  rtt=1.79ms rc=8(DSRtrMatchLabel) rsc=3 
     DS 1: ipaddr=10.10.4.4 ifaddr=10.10.4.4 iftype=ipv4Numbered MRU=1492 
           label[1]=3 protocol=5(OSPF)
           label[2]=262104 protocol=5(OSPF)
           label[3]=262139 protocol=2(BGP)
2  10.20.1.4  rtt=3.24ms rc=3(EgressRtr) rsc=3 
2  10.20.1.4  rtt=4.46ms rc=8(DSRtrMatchLabel) rsc=2 
     DS 1: ipaddr=10.10.9.6 ifaddr=10.10.9.6 iftype=ipv4Numbered MRU=1492 
           label[1]=3 protocol=5(OSPF)
           label[2]=262139 protocol=2(BGP)
3  10.20.1.6  rtt=6.24ms rc=3(EgressRtr) rsc=2 
3  10.20.1.6  rtt=6.18ms rc=3(EgressRtr) rsc=1 
*A:Dut-A#

BGP over SR-ISIS example output:

A:Dut-A# oam lsp-trace bgp-label prefix 11.21.1.6/32 detail downstream-map-tlv ddmap path-destination 127.1.1.1 
lsp-trace to 11.21.1.6/32: 0 hops min, 0 hops max, 168 byte packets
1  10.20.1.3  rtt=3.33ms rc=8(DSRtrMatchLabel) rsc=2 
    DS 1:  ipaddr=10.10.5.5 ifaddr=10.10.5.5 iftype=ipv4Numbered MRU=1496 
           label[1]=28506 protocol=6(ISIS)
           label[2]=262139 protocol=2(BGP)
     DS 2: ipaddr=10.10.11.4 ifaddr=10.10.11.4 iftype=ipv4Numbered MRU=1496 
           label[1]=28406 protocol=6(ISIS)
           label[2]=262139 protocol=2(BGP)
     DS 3: ipaddr=10.10.11.5 ifaddr=10.10.11.5 iftype=ipv4Numbered MRU=1496 
           label[1]=28506 protocol=6(ISIS)
           label[2]=262139 protocol=2(BGP)
2  10.20.1.4  rtt=5.12ms rc=8(DSRtrMatchLabel) rsc=2 
     DS 1: ipaddr=10.10.9.6 ifaddr=10.10.9.6 iftype=ipv4Numbered MRU=1492 
           label[1]=28606 protocol=6(ISIS)
           label[2]=262139 protocol=2(BGP)
3  10.20.1.6  rtt=8.41ms rc=3(EgressRtr) rsc=2 
3  10.20.1.6  rtt=6.93ms rc=3(EgressRtr) rsc=1

BGP over SR-TE (ISIS) example output:

*A:Dut-A# oam lsp-trace bgp-label prefix 11.21.1.6/32 detail downstream-map-tlv ddmap path-destination 127.1.1.1 
lsp-trace to 11.21.1.6/32: 0 hops min, 0 hops max, 248 byte packets
1  10.20.1.2  rtt=2.60ms rc=3(EgressRtr) rsc=4 
1  10.20.1.2  rtt=2.29ms rc=8(DSRtrMatchLabel) rsc=3 
     DS 1: ipaddr=10.10.4.4 ifaddr=10.10.4.4 iftype=ipv4Numbered MRU=1492 
           label[1]=3 protocol=6(ISIS)
           label[2]=262094 protocol=6(ISIS)
           label[3]=262139 protocol=2(BGP)
2  10.20.1.4  rtt=4.04ms rc=3(EgressRtr) rsc=3 
2  10.20.1.4  rtt=4.38ms rc=8(DSRtrMatchLabel) rsc=2 
     DS 1: ipaddr=10.10.9.6 ifaddr=10.10.9.6 iftype=ipv4Numbered MRU=1492 
           label[1]=3 protocol=6(ISIS)
           label[2]=262139 protocol=2(BGP)
3  10.20.1.6  rtt=6.64ms rc=3(EgressRtr) rsc=2 
3  10.20.1.6  rtt=5.94ms rc=3(EgressRtr) rsc=1

Assuming the topology in Figure: Example topology for BGP over SR-ISIS in inter-AS option C and BGP over SR-TE (ISIS) in inter-AS option C has the addition of an External Border Gateway Protocol (eBGP) peering between nodes B and C, the BGP IPv4 LSP spans the AS boundary and resolves to an SR-ISIS tunnel or an SR-TE LSP within each AS.

Figure: Example topology for BGP over SR-ISIS in inter-AS option C and BGP over SR-TE (ISIS) in inter-AS option C

BGP over SR-ISIS in inter-AS option C example output:

*A:Dut-A# oam lsp-trace bgp-label prefix 11.20.1.6/32 src-ip-address 11.20.1.1 detail downstream-map-tlv ddmap path-destination 127.1.1.1 
lsp-trace to 11.20.1.6/32: 0 hops min, 0 hops max, 168 byte packets
1  10.20.1.2  rtt=2.69ms rc=3(EgressRtr) rsc=2 
1  10.20.1.2  rtt=3.15ms rc=8(DSRtrMatchLabel) rsc=1 
     DS 1: ipaddr=10.10.3.3 ifaddr=10.10.3.3 iftype=ipv4Numbered MRU=0 
           label[1]=262127 protocol=2(BGP)
2  10.20.1.3  rtt=5.26ms rc=15(LabelSwitchedWithFecChange) rsc=1 
     DS 1: ipaddr=10.10.5.5 ifaddr=10.10.5.5 iftype=ipv4Numbered MRU=1496 
           label[1]=26506 protocol=6(ISIS)
           label[2]=262139 protocol=2(BGP)
           fecchange[1]=PUSH fectype=SR Ipv4 Prefix prefix=10.20.1.6 remotepeer=10.10.5.5 
3  10.20.1.5  rtt=7.08ms rc=8(DSRtrMatchLabel) rsc=2 
     DS 1: ipaddr=10.10.10.6 ifaddr=10.10.10.6 iftype=ipv4Numbered MRU=1496 
           label[1]=26606 protocol=6(ISIS)
       label[2]=262139 protocol=2(BGP)
4  10.20.1.6  rtt=9.41ms rc=3(EgressRtr) rsc=2 
4  10.20.1.6  rtt=9.53ms rc=3(EgressRtr) rsc=1

BGP over SR-TE (ISIS) in inter-AS option C example output:

*A:Dut-A# oam lsp-trace bgp-label prefix 11.20.1.6/32 src-ip-address 11.20.1.1 detail downstream-map-tlv ddmap path-destination 127.1.1.1 
lsp-trace to 11.20.1.6/32: 0 hops min, 0 hops max, 168 byte packets
1  10.20.1.2  rtt=2.77ms rc=3(EgressRtr) rsc=2 
1  10.20.1.2  rtt=2.92ms rc=8(DSRtrMatchLabel) rsc=1 
     DS 1: ipaddr=10.10.3.3 ifaddr=10.10.3.3 iftype=ipv4Numbered MRU=0 
           label[1]=262127 protocol=2(BGP)
2  10.20.1.3  rtt=4.82ms rc=15(LabelSwitchedWithFecChange) rsc=1 
     DS 1: ipaddr=10.10.5.5 ifaddr=10.10.5.5 iftype=ipv4Numbered MRU=1496 
           label[1]=26505 protocol=6(ISIS)
           label[2]=26506 protocol=6(ISIS)
           label[3]=262139 protocol=2(BGP)
           fecchange[1]=PUSH fectype=SR Ipv4 Prefix prefix=10.20.1.6            remotepeer=0.0.0.0 (Unknown)
           fecchange[2]=PUSH fectype=SR Ipv4 Prefix prefix=10.20.1.5            remotepeer=10.10.5.5 
3  10.20.1.5  rtt=7.10ms rc=3(EgressRtr) rsc=3 
3  10.20.1.5  rtt=7.45ms rc=8(DSRtrMatchLabel) rsc=2 
     DS 1: ipaddr=10.10.10.6 ifaddr=10.10.10.6 iftype=ipv4Numbered MRU=1496 
           label[1]=26606 protocol=6(ISIS)
           label[2]=262139 protocol=2(BGP)
4  10.20.1.6  rtt=9.23ms  c=3(EgressRtr) rsc=2 
4  10.20.1.6  rtt=9.46ms rc=3(EgressRtr) rsc=1 
*A:Dut-A
Parent topic: MPLS OAM support in Segment Routing