In order for the maximum length service frame to successfully travel from a local ingress SAP to a remote egress SAP, the MTU values configured on the local ingress SAP, the SDP (GRE or MPLS), and the egress SAP must be coordinated to accept the maximum frame size the service can forward. For example, the targeted MTU values to configure for a distributed Epipe service (ALA-A and ALA-B) are shown in Figure 1.
Because ALA-A uses Dot1q encapsulation, the SAP MTU must be set to 1518 to be able to accept a 1514 byte service frame (see Table 1 for MTU default values). Each SDP MTU must be set to at least 1514 as well. If ALA-A’s network port (2/1/1) is configured as an Ethernet port with a GRE SDP encapsulation type, then the MTU value of network ports 2/1/1 and 3/1/1 must each be at least 1556 bytes (1514 MTU + 28 GRE/Martini + 14 Ethernet). Finally, the MTU of ALA-B’s SAP (access port 4/1/1) must be at least 1514, as it uses null encapsulation.
Table 1 shows example MTU configuration values.
ALA-A |
ALA-B |
|||
|---|---|---|---|---|
Access (SAP) |
Network |
Network |
Access (SAP) |
|
Port (slot/MDA/port) |
1/1/1 |
2/1/12 |
3/1/1 |
4/1/1 |
Mode or ECAP-type |
dot1q |
network |
network |
null |
MTU |
1518 |
1556 |
1556 |
1514 |