Interop MTUs

Inter-op MTU sizes. The "Usable MTU" represents the maximum size for the payload part of an Ethernet frame.

+---------------------------+----------------------------+-----------------------+--------------------------+-----------------+
| Device Tested On          | Includes Ethernet headers  | Includes MPLS headers | Configured interface MTU | L2 Payload Size |
|                           |       in MTU setting       |                       | (PHY interface)          |                 |
+---------------------------+----------------------------+-----------------------+--------------------------+-----------------+
| Alcatel TiMOS 7210-SASX   | Y                          | Y                     | 9014                     | 9000            |
| Arista EOS 7280CR3K **MTU | N                          | Y                     | 9214                     | 9214            |
| Arista EOS 7280CR3K **MRU | Y                          | Y                     | 9214 *inc CRC            | 9196            |
| Cisco IOS 7600            | N                          | Y                     | 9000                     | 9000            |
| Cisco IOS-XE CSR1kv subint| N                          | ?                     | 9000                     | 9000            |
| Cisco IOS-XR ASR9K        | Y                          | N                     | 9014                     | 9000            |
| Huawei VRP CX600          | N                          | ?                     | 9000                     | 9000            |
| Juniper JUNOS MX480       | Y                          | Y                     | 9014                     | 9000            |
+---------------------------+----------------------------+-----------------------+--------------------------+-----------------+

Inter-op ping command sizes. The IOS ping command will account the Ethernet headers, IOS-XR command expects them to be removed, Junos expects all headers upto the ICMP payload to be removed.

+---------------------------------+----------------------------+-------------------------------------+
| Device Tested On                |    MTU size on phy         |    Max size usable with             |
|                                 |    interface               |    "ping" cmd and df-bit            |
+---------------------------------+----------------------------+-------------------------------------+
| Alcatel TiMOS (7210-SASX)       | 9000                       | 8958 (-14 Ethernet, -20 IP, -8 ICMP)|
| Arista EOS 7280CR3K             | 1500                       | 1500                                |
| Cisco IOS (7600)                | 9000                       | 9000                                |
| Cisco IOS-XE (CSR1000v sub-int) | 9000                       | 9000                                |
| Cisco IOS-XR (ASR9K/NCS5K/NCS6K)| 9014                       | 9000 (-14 Ethernet) *1              |
| Huawei VRP (CX600)              | 9000                       | 8972 (-20 IP, -8 ICMP)              |
| Juniper JUNOS (MX480)           | 9000                       | 8958 (-14 Ethernet, -20 IP, -8 ICMP)|
| Linux (3.2.0-4-amd64)           | 1500                       | 1472 (-20 IP, -8 ICMP)              |
| Mac OS X 10.13.6(Darwin 17.7.0) | 1500                       | 1472 (-20 IP, -8 ICMP)              |
+---------------------------------+----------------------------+-------------------------------------+

*1 If using MPLS explicit null then max ping size is 8996, -14 for Ethernet and -4 for the MPLS explicit null label.

In the table below we can see the impact of tagged VLAN sub-interfaces. IOS ignores Ethernet headers including VLAN tags in the MTU value set at an interface (meaning that it always offers the layer 3 protocol 1500 bytes of transport, even if one configures a dot1q tag, IOS sends 1518 byte frames instead of 1514 byte frames). IOS-XR has the same behaviour as IOS.

+----------------------------+----------------------------+-------------------------------------+----------------------------+
| Device Tested On           |    MTU size on phy         |    Max size usable with "ping" cmd  | L2 Packet size on the wire |
|                            |    interface               |    and df-bit from VLAN sub-int     |                            |
+----------------------------+----------------------------+-------------------------------------+----------------------------+
| Arista EOS 7280CR3K        | 1500 (default)             | 1500                                | 1518                       |
| Cisco IOS (7200)           | 1500 (default)             | 1500                                | 1518                       |
| Cisco IOS (7600)           | 1500 (default)             | 1500                                | 1518                       |
| Cisco IOS-XE (CSR1000v)    | 1500 (default)             | 1500                                | 1518                       |
| Cisco IOS-XR (ASR9K)       | 1514 (default, inc Headers)| 1500 (-14 Ethernet, -4 VLAN)        | 1518                       |
+----------------------------+----------------------------+-------------------------------------+----------------------------+

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