H3C SR6600 Command Reference Manual page 11

Adjacency SID-based packet forwarding
Figure 4 shows how a packet is forwarded along the SRLSP from Device A to Device E based on
adjacency SIDs. In this example, the label stack for the packet is configured as (200, 201, 202, and
203) on Device A.
1. Ingress node Device A searches for a forwarding entry for the top label (200) to determine the
next hop. Then, Device A adds label stack (201, 202, and 203) to the packet, and forwards the
packet to the next hop (Device B).
2. When transit node Device B receives the packet, it searches for a forwarding entry for the top
label (201) to determine the next hop. Then, Device B removes the top label from the stack and
forwards the packet to the next hop (Device C).
3. When transit node Device C receives the packet, it searches for a forwarding entry for the top
label (202) to determine the next hop. Then, Device C removes the top label from the stack and
forwards the packet to the next hop (Device D).
4. When transit node Device D receives the packet, it searches for a forwarding entry for the label
(203) to determine the next hop. Then, Device D removes the label stack from the packet and
forwards the packet to the next hop (Device E).
5. When egress node Device E receives the packet, it forwards the packet by IP address.
Figure 4 Adjacency SID-based packet forwarding
Device A
In Label Nexthop
200 Device B
Prefix and adjacency SID-based packet forwarding
Figure 5 shows how a packet is forwarded along the SRLSP from Device A to Device E based on
prefix SIDs and adjacency SIDs. In this example, the index value for the prefix SID of Device C is 1.
The prefix SIDs for Device A, Device B, and Device C are 18001, 17001, and 16001, respectively.
The Adjacency SIDs that Device C and Device D allocate for the adjacent links are 16 and 17,
respectively. On Device A, the label stack for the packet is (18001, 16, 17).
1. Ingress node Device A searches for a forwarding entry for label 18001 to determine the
outgoing label (17001) and next hop (Device B). Device A swaps label 18001 with 17001. Then,
it adds label stack (17001, 16, 17) to the packet and sends the packet to the next hop (Device
B).
2. When transit node Device B receives the packet, it searches for a label forwarding entry that
matches the top label in the label stack (17001). Then, Device B uses the outgoing label of the
matched entry (16001) to replace the top label and forwards the packet to the next hop (Device
C).
3. When transit node Device C receives the packet, it removes the top label 16001 and searches
for a forwarding entry for the next label (16) to determine the next hop. Then, Device C removes
label 16 from the stack and forwards the packet to the next hop (Device D).
4. When transit node Device D receives the packet, it searches for a forwarding entry for the label
(17) to determine the next hop. Then, Device D removes the label stack from the packet and
forwards the packet to the next hop (Device E).
5. When egress node Device E receives the packet, it forwards the packet by IP address.
201
202
203
IP data IP data
Device B
In Label Nexthop
201 Device C
202
203
203
IP data
Device C
In Label Nexthop
202 Device D
5
IP data
Device D
In Label Nexthop
203 Device E
Device E