Table of Contents
Advertisement
Configuring the MPLS Module
Configuring the Maximum Transmission Unit Size
After you have enabled MPLS, you can configure the maximum transmission unit
(MTU) size using the following command:
config mpls vlan [<name> | all] ip-mtu <number>
This command configures the IP MTU for frames transmitted onto MPLS LSPs via the
specified egress VLAN. The default settings is 1496 bytes. If
configuring MTU applies to all MPLS-enabled VLANs.
This command applies to the ingress LSR only when a received IP packet is destined for
an MPLS LSP. In this case, if the length of the IP packet exceeds the configured MTU
size for the egress VLAN and the Don't Fragment (DF) bit is not set in the IP header of
the packet, the packet is fragmented before it is forwarded onto an MPLS LSP. If the DF
bit is set in the packet header, Path MTU Discovery starts.
Fragmentation is based on either the minimum value of the configured MPLS IP MTU
size or the configured IP MTU size for the egress VLAN. (The IP MTU size is
configured using the
You should configure the MPLS IP MTU so that the addition of the MPLS label stack
the link layer header does not cause the packet to be too large to be transmitted on the
egress ports. To avoid potential problems, you should enable jumbo frame support on
all ports that are members of an MPLS VLAN.
Configuring the Propagation of IP TTL
To enable or disable the propagation of the IP time-to-live (TTL) function, use the
following command:
config mpls propagate-ip-ttl [enabled | disabled]
This command enables and disables the propagation of the IP TTL value for routed IP
packets. The default setting is enabled.
You must maintain identical
MPLS domain. Not doing so may cause packets to loop endlessly and not be
purged from the network if a routing loop is inadvertently introduced.
When
propagate-ip-ttl
between the ingress LSR and the egress LSR. Intermediate LSRs in the MPLS network
are not viewed as router hops (from an IP TTL perspective). In this case, the IP TTL is
3-16
config ip-mtu <number> vlan <name>
propagate-ip-ttl
is disabled, the LSP is viewed as a point-to-point link
is selected, the
all
command.)
settings on all LERs in the
MPLS Module Installation and User Guide
Advertisement
Table of Contents
