How does a router know the MTU of a network?
I've done several exercises where you're given the MTU of a net or subnet, but I wonder how routers know the MTU of the nets they're connected. I've learnt that in OSPF protocol this information is excanged among routers. However, is there another way of finding that information for a router that doesn't use OSPF?
I hope someone can help me. Thank you for your responses.
routing router layer1 interface mtu
edited 18 mins ago
Ron Maupin♦
62.8k1365120
asked 59 mins ago
Josemi Josemi
202
add a comment |
I've done several exercises where you're given the MTU of a net or subnet, but I wonder how routers know the MTU of the nets they're connected. I've learnt that in OSPF protocol this information is excanged among routers. However, is there another way of finding that information for a router that doesn't use OSPF?
I hope someone can help me. Thank you for your responses.
routing router layer1 interface mtu
edited 18 mins ago
Ron Maupin♦
62.8k1365120
asked 59 mins ago
Josemi Josemi
202
add a comment |
I've done several exercises where you're given the MTU of a net or subnet, but I wonder how routers know the MTU of the nets they're connected. I've learnt that in OSPF protocol this information is excanged among routers. However, is there another way of finding that information for a router that doesn't use OSPF?
I hope someone can help me. Thank you for your responses.
routing router layer1 interface mtu
edited 18 mins ago
Ron Maupin♦
62.8k1365120
asked 59 mins ago
Josemi Josemi
202
I've done several exercises where you're given the MTU of a net or subnet, but I wonder how routers know the MTU of the nets they're connected. I've learnt that in OSPF protocol this information is excanged among routers. However, is there another way of finding that information for a router that doesn't use OSPF?
I hope someone can help me. Thank you for your responses.
routing router layer1 interface mtu
routing router layer1 interface mtu
edited 18 mins ago
Ron Maupin♦
62.8k1365120
asked 59 mins ago
Josemi Josemi
202
edited 18 mins ago
Ron Maupin♦
62.8k1365120
asked 59 mins ago
Josemi Josemi
202
edited 18 mins ago
Ron Maupin♦
62.8k1365120
edited 18 mins ago
Ron Maupin♦
62.8k1365120
edited 18 mins ago
Ron Maupin♦
62.8k1365120
62.8k1365120
asked 59 mins ago
Josemi Josemi
202
asked 59 mins ago
Josemi Josemi
202
asked 59 mins ago
Josemi Josemi
202
202
add a comment |
add a comment |
2 Answers
2
active
oldest
votes
The MTU of an interface is a function of the layer-2 protocol for that interface, and a device, including a router, will inherently know the MTU of the interface based on the protocol for the interface. For example the MTU for ethernet is 1500.
Some routers can configure the interface MTU with a configuration command. Also virtual interfaces, e.g. a tunnel, will calculate the MTU based on the MTU of the physical interface that is the source of the tunnel, minus the tunnel protocol overhead.
For Cisco routers, you can use the show interfaces command to see the MTU for one or more interfaces. Other vendors will have similar commands.
answered 52 mins ago
Ron Maupin♦Ron Maupin
62.8k1365120
add a comment |
Routers know because they have physical interfaces connected to the networks. Those interfaces are configured for the correct MTU.
You are mistaken about OSPF: The protocol does not exchange MTU information.
answered 52 mins ago
Ron TrunkRon Trunk
34.9k23272
I think the OSPF confusion is that the MTU must match for OSPF to form a neighbor.
– Ron Maupin♦
51 mins ago
I don't think so, if you consult the rfc of OSPF, version 2: rfc-editor.org/pdfrfc/rfc2328.txt.pdf , in page 195 where the information database packet is described, there is a field ofinterface MTU.
– Josemi
37 mins ago
add a comment |
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2 Answers
2
active
oldest
votes
2 Answers
2
active
oldest
votes
active
oldest
votes
active
oldest
votes
The MTU of an interface is a function of the layer-2 protocol for that interface, and a device, including a router, will inherently know the MTU of the interface based on the protocol for the interface. For example the MTU for ethernet is 1500.
Some routers can configure the interface MTU with a configuration command. Also virtual interfaces, e.g. a tunnel, will calculate the MTU based on the MTU of the physical interface that is the source of the tunnel, minus the tunnel protocol overhead.
For Cisco routers, you can use the show interfaces command to see the MTU for one or more interfaces. Other vendors will have similar commands.
answered 52 mins ago
Ron Maupin♦Ron Maupin
62.8k1365120
add a comment |
The MTU of an interface is a function of the layer-2 protocol for that interface, and a device, including a router, will inherently know the MTU of the interface based on the protocol for the interface. For example the MTU for ethernet is 1500.
Some routers can configure the interface MTU with a configuration command. Also virtual interfaces, e.g. a tunnel, will calculate the MTU based on the MTU of the physical interface that is the source of the tunnel, minus the tunnel protocol overhead.
For Cisco routers, you can use the show interfaces command to see the MTU for one or more interfaces. Other vendors will have similar commands.
answered 52 mins ago
Ron Maupin♦Ron Maupin
62.8k1365120
add a comment |
The MTU of an interface is a function of the layer-2 protocol for that interface, and a device, including a router, will inherently know the MTU of the interface based on the protocol for the interface. For example the MTU for ethernet is 1500.
Some routers can configure the interface MTU with a configuration command. Also virtual interfaces, e.g. a tunnel, will calculate the MTU based on the MTU of the physical interface that is the source of the tunnel, minus the tunnel protocol overhead.
For Cisco routers, you can use the show interfaces command to see the MTU for one or more interfaces. Other vendors will have similar commands.
answered 52 mins ago
Ron Maupin♦Ron Maupin
62.8k1365120
The MTU of an interface is a function of the layer-2 protocol for that interface, and a device, including a router, will inherently know the MTU of the interface based on the protocol for the interface. For example the MTU for ethernet is 1500.
Some routers can configure the interface MTU with a configuration command. Also virtual interfaces, e.g. a tunnel, will calculate the MTU based on the MTU of the physical interface that is the source of the tunnel, minus the tunnel protocol overhead.
For Cisco routers, you can use the show interfaces command to see the MTU for one or more interfaces. Other vendors will have similar commands.
answered 52 mins ago
Ron Maupin♦Ron Maupin
62.8k1365120
answered 52 mins ago
Ron Maupin♦Ron Maupin
62.8k1365120
answered 52 mins ago
Ron Maupin♦Ron Maupin
62.8k1365120
answered 52 mins ago
Ron Maupin♦Ron Maupin
62.8k1365120
62.8k1365120
add a comment |
add a comment |
Routers know because they have physical interfaces connected to the networks. Those interfaces are configured for the correct MTU.
You are mistaken about OSPF: The protocol does not exchange MTU information.
answered 52 mins ago
Ron TrunkRon Trunk
34.9k23272
I think the OSPF confusion is that the MTU must match for OSPF to form a neighbor.
– Ron Maupin♦
51 mins ago
I don't think so, if you consult the rfc of OSPF, version 2: rfc-editor.org/pdfrfc/rfc2328.txt.pdf , in page 195 where the information database packet is described, there is a field ofinterface MTU.
– Josemi
37 mins ago
add a comment |
Routers know because they have physical interfaces connected to the networks. Those interfaces are configured for the correct MTU.
You are mistaken about OSPF: The protocol does not exchange MTU information.
answered 52 mins ago
Ron TrunkRon Trunk
34.9k23272
I think the OSPF confusion is that the MTU must match for OSPF to form a neighbor.
– Ron Maupin♦
51 mins ago
I don't think so, if you consult the rfc of OSPF, version 2: rfc-editor.org/pdfrfc/rfc2328.txt.pdf , in page 195 where the information database packet is described, there is a field ofinterface MTU.
– Josemi
37 mins ago
add a comment |
Routers know because they have physical interfaces connected to the networks. Those interfaces are configured for the correct MTU.
You are mistaken about OSPF: The protocol does not exchange MTU information.
answered 52 mins ago
Ron TrunkRon Trunk
34.9k23272
Routers know because they have physical interfaces connected to the networks. Those interfaces are configured for the correct MTU.
You are mistaken about OSPF: The protocol does not exchange MTU information.
answered 52 mins ago
Ron TrunkRon Trunk
34.9k23272
answered 52 mins ago
Ron TrunkRon Trunk
34.9k23272
answered 52 mins ago
Ron TrunkRon Trunk
34.9k23272
answered 52 mins ago
Ron TrunkRon Trunk
34.9k23272
34.9k23272
I think the OSPF confusion is that the MTU must match for OSPF to form a neighbor.
– Ron Maupin♦
51 mins ago
I don't think so, if you consult the rfc of OSPF, version 2: rfc-editor.org/pdfrfc/rfc2328.txt.pdf , in page 195 where the information database packet is described, there is a field ofinterface MTU.
– Josemi
37 mins ago
add a comment |
I think the OSPF confusion is that the MTU must match for OSPF to form a neighbor.
– Ron Maupin♦
51 mins ago
I don't think so, if you consult the rfc of OSPF, version 2: rfc-editor.org/pdfrfc/rfc2328.txt.pdf , in page 195 where the information database packet is described, there is a field ofinterface MTU.
– Josemi
37 mins ago
I think the OSPF confusion is that the MTU must match for OSPF to form a neighbor.
– Ron Maupin♦
51 mins ago
I think the OSPF confusion is that the MTU must match for OSPF to form a neighbor.
– Ron Maupin♦
51 mins ago
I don't think so, if you consult the rfc of OSPF, version 2: rfc-editor.org/pdfrfc/rfc2328.txt.pdf , in page 195 where the information database packet is described, there is a field of
interface MTU.– Josemi
37 mins ago
I don't think so, if you consult the rfc of OSPF, version 2: rfc-editor.org/pdfrfc/rfc2328.txt.pdf , in page 195 where the information database packet is described, there is a field of
interface MTU.– Josemi
37 mins ago
add a comment |
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