Arista EOS Segment Routing (2) - MPLS Ping to verify SR data plane

With the same topology, to verify the SR data plane, we can use the command - "ping mpls" to have PE1 send a UDP packet with the correct label. 

PE1#ping mpls segment-routing ip 4.4.4.4/32 repeat 1
LSP ping to Segment-Routing route 4.4.4.4/32
   timeout is 5000ms, interval is 1000ms
Via 10.1.2.2, Ethernet2/4, label stack (top label first): [900004]
   Reply from 10.3.4.4: seq=1, time=0.53ms, success: egress ok

--- Segment-Routing target fec 4.4.4.4/32 : lspping statistics ---
Via 10.1.2.2, Ethernet2/4, label stack (top label first): [900004]
   1 packets transmitted, 1 received, 0% packet loss, time 150ms
   1 received from 10.3.4.4, rtt min/max/avg 0.530/0.530/0.530 ms

Turning on tcpdump on P1, it shows the following packets:

P1#sh run | grep moni
monitor session sr source Ethernet54/4
monitor session sr destination Cpu

P1#bash tcpdump -nvvvi mirror1 udp or mpls
tcpdump: listening on mirror1, link-type EN10MB (Ethernet), capture size 262144 bytes
13:48:15.934459 44:4c:a8:97:77:21 > 44:4c:a8:97:8c:51, ethertype MPLS unicast (0x8847), length 98: MPLS (label 900004, exp 0, [S], ttl 255)
(tos 0x0, ttl 1, id 0, offset 0, flags [DF], proto UDP (17), length 80, options (RA))
    10.1.2.1.36260 > 127.0.0.1.lsp-ping:
LSP-PINGv1, msg-type: MPLS Echo Request (1), length: 48
  reply-mode: Reply via an IPv4/IPv6 UDP packet (2)
  Return Code: No return code or return code contained in the Error Code TLV (0)
  Return Subcode: (0)
  Sender Handle: 0x00000000, Sequence: 1
  Sender Timestamp: -16:-39:-45.54962696 Receiver Timestamp: no timestamp
  Target FEC Stack TLV (1), length: 12
    Unknown subTLV (31744), length: 6
      0x0000:  0404 0404 2002
    0x0000:  7c00 0006 0404 0404 2002 0000
13:48:15.934737 44:4c:a8:97:8c:51 > 44:4c:a8:97:77:21, ethertype IPv4 (0x0800), length 74: (tos 0x0, ttl 62, id 36448, offset 0, flags [DF], proto UDP (17), length 60)
    10.3.4.4.lsp-ping > 10.1.2.1.36260:
LSP-PINGv1, msg-type: MPLS Echo Reply (2), length: 32
  reply-mode: Reply via an IPv4/IPv6 UDP packet (2)
  Return Code: Replying router is an egress for the FEC at stack depth 1 (3)
  Return Subcode: (1)
  Sender Handle: 0x00000000, Sequence: 1
  Sender Timestamp: -16:-39:-45.54962696 Receiver Timestamp: -16:-40:-1.401478080

From the above packet capture, 

• The icmp echo request is encap'ed in MPLS packet with label 90004 as expected. 
• The dest address of inner ip is 127.0.0.1. With destination address on network 127, the packet can't be routed if LSP is broken before the final destination and the packet is decap'ed prematurely. 
• The icmp echo reply is just a native ipv4 packet.