MPLS-TE Path Message Behavior

When employing MPLS-TE, RSVP is used to establish and maintain the paths of the TE tunnels. RSVP will send periodic Path Messages to refresh the path. These messages operate outside of the tunnel, but are sent down the tunnel path.

The tunnel path is used for both RSVP messages and actual user traffic. User traffic is encapsulated with the tunnel, while RSVP messages are outside of the tunnel.

Wireshark Captures

RSVP

Here is a capture of RSVP between two PE routers that are in the tunnel path:

Frame 3: 238 bytes on wire (1904 bits), 238 bytes captured (1904 bits)
Ethernet II, Src: 52:54:00:1c:25:7e (52:54:00:1c:25:7e), Dst: 52:54:00:0a:df:6b (52:54:00:0a:df:6b)
Internet Protocol Version 4, Src: 2.2.2.2, Dst: 6.6.6.6
Resource ReserVation Protocol (RSVP): PATH Message. SESSION: IPv4-LSP, Destination 6.6.6.6, Short Call ID 0, Tunnel ID 1, Ext ID 2020202. SENDER TEMPLATE: IPv4-LSP, Tunnel Source: 2.2.2.2, Short Call ID: 0, LSP ID: 9.
    RSVP Header. PATH Message.
    SESSION: IPv4-LSP, Destination 6.6.6.6, Short Call ID 0, Tunnel ID 1, Ext ID 2020202.
    HOP: IPv4, 192.168.45.4
    TIME VALUES: 30000 ms
    EXPLICIT ROUTE: IPv4 192.168.45.5, IPv4 192.168.56.5, IPv4 192.168.56.6,
    LABEL REQUEST: Basic: L3PID: IPv4 (0x0800)
    SESSION ATTRIBUTE: SetupPrio 7, HoldPrio 7, SE Style,  [PE1_t1]
    SENDER TEMPLATE: IPv4-LSP, Tunnel Source: 2.2.2.2, Short Call ID: 0, LSP ID: 9.
    SENDER TSPEC: IntServ, Token Bucket, 93750 bytes/sec.
    ADSPEC

User Traffic

Here is a capture of user traffic that was captured between two PE routers that are in the tunnel path:

Frame 4: 118 bytes on wire (944 bits), 118 bytes captured (944 bits)
Ethernet II, Src: 52:54:00:1c:25:7e (52:54:00:1c:25:7e), Dst: 52:54:00:0a:df:6b (52:54:00:0a:df:6b)
MultiProtocol Label Switching Header, Label: 29, Exp: 0, S: 1, TTL: 253
    0000 0000 0000 0001 1101 .... .... .... = MPLS Label: 29 (0x0001d)
    .... .... .... .... .... 000. .... .... = MPLS Experimental Bits: 0
    .... .... .... .... .... ...1 .... .... = MPLS Bottom Of Label Stack: 1
    .... .... .... .... .... .... 1111 1101 = MPLS TTL: 253
Internet Protocol Version 4, Src: 1.1.1.1, Dst: 7.7.7.7
    0100 .... = Version: 4
    .... 0101 = Header Length: 20 bytes (5)
    Differentiated Services Field: 0x00 (DSCP: CS0, ECN: Not-ECT)
    Total Length: 100
    Identification: 0x0005 (5)
    000. .... = Flags: 0x0
    ...0 0000 0000 0000 = Fragment Offset: 0
    Time to Live: 254
    Protocol: ICMP (1)
    Header Checksum: 0xac84 [validation disabled]
    [Header checksum status: Unverified]
    Source Address: 1.1.1.1
    Destination Address: 7.7.7.7
Internet Control Message Protocol
    Type: 8 (Echo (ping) request)
    Code: 0
    Checksum: 0x9f83 [correct]
    [Checksum Status: Good]
    Identifier (BE): 1 (0x0001)
    Identifier (LE): 256 (0x0100)
    Sequence Number (BE): 0 (0x0000)
    Sequence Number (LE): 0 (0x0000)
    [No response seen]
    Data (72 bytes)

https://networklessons.com/mpls/mpls-te-autoroute-announce