Date created: Monday, March 2, 2015 4:09:51 PM. Last modified: Sunday, March 31, 2024 3:46:25 PM

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 | +----------------------------+----------------------------+-------------------------------------+----------------------------+