2. Upon receiving the UDP packet with the Hop Limit value in the IPv6 packet header being 0, the intermediate node sends an ICMPv6 timeout message to Device A.
3. Upon receiving the ICMPv6 timeout message, Device A sends another UDP packet by adding the Hop limit value by 1.
4. Upon receiving the UDP packet with the Hop Limit value in the IPv6 packet header not being 0, the intermediate node forwards the UDP packet as follows:
On an SRv6 capable node (such as Device B):
The node forwards the UDP packet based on the SRH if the packet destination IPv6 address is the local SRv6 SID.
On an SRv6 incapable node (such as Device C):
The node forwards the UDP packet according to routing table lookup.
5. Upon receiving the UDP packet (with Hop Limit 0 in the IPv6 packet header and SL=0 in the
SRH), Device D verifies the packet destination IPv6 address.
If the IPv6 address is the local SRv6 SID, the verification succeeds, and Device D sends an
ICMPv6 port unreachable message to Device A.
If the IPv6 address is not the local SRv6 SID, the verification fails, and Device D discards the UDP packet.
6. Device A determines whether the destination node is reachable based on reception of the
ICMPv6 port unreachable message:
If the ICMPv6 port unreachable message is received before the specified timeout timer expires, the destination node is reachable. The tracert result displays the SRv6 path from the source node to the destination node.
If no ICMPv6 port unreachable message is received when the specified timeout timer expires, the destination node is unreachable. You can locate the faulty node based on the tracert result.
SRv6 TE policy-based ping
Use SRv6 TE policy-based ping to detect reachability of each node in an SRv6 TE policy.
Figure 87 SRv6 TE policy-based ping
IPv6 SA=a, IPv6 DA=b
SRH[(d, b) SL=1]
ICMPv6 Echo Request
A
SRv6 SID=a
B
SRv6 SID=b
C D
SRv6 SID=d
IPv6 SA=b, IPv6 DA=d
SRH[(d, b) SL=0]
ICMPv6 Echo Request
In Figure 87 , the SID list of the SRv6 TE policy contains {b, d}. The SRv6 TE policy-based ping
process is as follows:
1. Device A initiates a ping to Device D. It constructs an ICMPv6 echo request encapsulated with an SRH (that contains the SID list of the SRv6 TE policy) and then forwards the request.
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