Information Technology Reference
In-Depth Information
The words
tag
,
label
, and
MPLS
are often used interchangeably in CLI and command
outputs.
NOTE
Table 10-4 shows a similar LIB on R4, except that R4 assigns 20 to 192.168.100.5/32 and
21 to 192.168.100.6/32.
Table 10-4
Label Bindings on R4
Prefix
Local Label
Received Label
Next Hop
192.168.100.5/32
20
Implicit Null
R5
192.168.100.6/32
21
20
R5
On R2, two paths are received for the two prefixes—one via R3 and one via R4. Table 10-5
shows the LIB on R2. For 192.168.100.5/32, for example, R2 receives label 20 from R4 and
label 21 from R3. Note that the same label value 21 is received from R4 for 192.168.100.6/32.
This is fine, because R2 keeps track of the bindings for each prefix in relation to the
neighbor that advertises the label.
Table 10-5
Label Bindings on R2
Prefix
Local Label
Received Label
Next Hop
192.168.100.5/32
20
20
R4
21
R3
192.168.100.6/32
21
21
R4
22
R3
To summarize, there are two LSPs for each prefix from R2 (ingress) to R5 (egress): one
from R2 to R5 via R3, and one from R2 to R5 via R4. Because the path cost is the same
between these two LSPs, traffic is load-shared. This is shown in Example 10-6.
Example 10-6
Output of
traceroute
for 192.168.100.6 on R2
R2#traceroute 192.168.100.6
Type escape sequence to abort.
Tracing the route to 192.168.100.6
1 192.168.24.4 [MPLS: Label 21 Exp 0] 32 msec
192.168.23.3 [MPLS: Label 22 Exp 0] 52 msec
192.168.24.4 [MPLS: Label 21 Exp 0] 40 msec
continues
