Traceroute Or Pathtrace Message - Cisco Nexus 9000 Series Configuration Manual

Configuring VXLAN OAM

Traceroute or Pathtrace Message

• From Leaf 1 (VTEP 1) to VM 2 (host attached to another VTEP) (ICMP or NVO3 draft Tissa channel)
Figure 11: Loopback Message

Traceroute or Pathtrace Message

The traceroute or pathtrace message is used for the fault isolation. In a VXLAN network, it may be desirable
to find the list of switches that are traversed by a frame to reach the destination. When the loopback test from
a source switch to a destination switch fails, the next step is to find out the offending switch in the path. The
operation of the path trace message begins with the source switch transmitting a VXLAN OAM frame with
a TTL value of 1. The next hop switch receives this frame, decrements the TTL, and on finding that the TTL
is 0, it transmits a TTL expiry message to the sender switch. The sender switch records this message as an
indication of success from the first hop switch. Then the source switch increases the TTL value by one in the
next path trace message to find the second hop. At each new transmission, the sequence number in the message
is incremented. Each intermediate switch along the path decrements the TTL value by 1 as is the case with
regular VXLAN forwarding.
This process continues until a response is received from the destination switch, or the path trace process
timeout occurs, or the hop count reaches a maximum configured value. The payload in the VXLAN OAM
frames is referred to as the flow entropy. The flow entropy can be populated so as to choose a particular path
among multiple ECMP paths between a source and destination switch. The TTL expiry message may also be
generated by the intermediate switches for the actual data frames. The same payload of the original path trace
request is preserved for the payload of the response.
Cisco Nexus 9000 Series NX-OS VXLAN Configuration Guide, Release 7.x
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