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tunnel command

what are these commands means?

ip mtu 1500

ip pim sparse-dense-mode

ip tcp adjust-mss 1436

ip ospf message-digest-key 1 xxx

ip ospf cost 100

ip ospf mtu-ignore

1 ACCEPTED SOLUTION

Accepted Solutions

Re: tunnel command

Hi Friend,

1) ip mtu 1500

To set the maximum transmission unit (MTU) size of IP packets sent on an interface use this command.

If an IP packet exceeds the MTU set for the interface, the Cisco IOS software will fragment it.

All devices on a physical medium must have the same protocol MTU in order to operate.

Changing the MTU value (with the mtu interface configuration command) can affect the IP MTU value. If the current IP MTU value is the same as the MTU value, and you change the MTU value, the IP MTU value will be modified automatically to match the new MTU. However, the reverse is not true; changing the IP MTU value has no effect on the value for the mtu command.

ip mtu 1500 sets the maximum IP packet size for the interface to 1500 bytes

2) ip pim sparse-dense-mode

To enable Protocol Independent Multicast (PIM) on an interface, use the ip pim command in interface configuration mode.

sparse-dense-mode --> Treats the interface in either sparse mode or dense mode of operation, depending on which mode the multicast group operates in.

For complete usage guide lines check this link

http://www.cisco.com/univercd/cc/td/doc/product/software/ios124/124tcr/timc_r/mlt_i2ht.htm#wp1080424

3) ip tcp adjust-mss 1436

To adjust the maximum segment size (MSS) value of TCP SYN packets going through a router, ip tcp adjust-mss command is used in interface configuration mode.

Check this link for more details

http://www.cisco.com/univercd/cc/td/doc/product/software/ios124/124tcr/tiap_r/apl_i2ht.htm#wp1198919

4) ip ospf message-digest-key 1 md5 7 15171D091633

To enable Open Shortest Path First (OSPF) Message Digest 5 (MD5) authentication this command is used.

Usually, one key per interface is used to generate authentication information when sending packets and to authenticate incoming packets. The same key identifier on the neighbor router must have the same key value

Check this link for more details

http://www.cisco.com/univercd/cc/td/doc/product/software/ios124/124tcr/tirp_r/rteospht.htm#wp1118475

5) ip ospf cost 100

To explicitly specify the cost of sending a packet on an interface, use the ip ospf cost command in interface configuration mode.

Have a look at this link for more details

http://www.cisco.com/univercd/cc/td/doc/product/software/ios124/124tcr/tirp_r/rteospht.htm#wp1117886

6) ip ospf mtu-ignore

To disable Open Shortest Path First (OSPF) maximum transmission unit (MTU) mismatch detection on receiving Database Descriptor (DBD) packets, ip ospf mtu-ignore command is used in interface configuration mode

OSPF checks whether neighbors are using the same MTU on a common interface. This check is performed when neighbors exchange DBD packets. If the receiving MTU in the DBD packet is higher than the IP MTU configured on the incoming interface, OSPF adjacency will not be established

HTH, if yes please rate the post.

Ankur

2 REPLIES

Re: tunnel command

Hi Friend,

1) ip mtu 1500

To set the maximum transmission unit (MTU) size of IP packets sent on an interface use this command.

If an IP packet exceeds the MTU set for the interface, the Cisco IOS software will fragment it.

All devices on a physical medium must have the same protocol MTU in order to operate.

Changing the MTU value (with the mtu interface configuration command) can affect the IP MTU value. If the current IP MTU value is the same as the MTU value, and you change the MTU value, the IP MTU value will be modified automatically to match the new MTU. However, the reverse is not true; changing the IP MTU value has no effect on the value for the mtu command.

ip mtu 1500 sets the maximum IP packet size for the interface to 1500 bytes

2) ip pim sparse-dense-mode

To enable Protocol Independent Multicast (PIM) on an interface, use the ip pim command in interface configuration mode.

sparse-dense-mode --> Treats the interface in either sparse mode or dense mode of operation, depending on which mode the multicast group operates in.

For complete usage guide lines check this link

http://www.cisco.com/univercd/cc/td/doc/product/software/ios124/124tcr/timc_r/mlt_i2ht.htm#wp1080424

3) ip tcp adjust-mss 1436

To adjust the maximum segment size (MSS) value of TCP SYN packets going through a router, ip tcp adjust-mss command is used in interface configuration mode.

Check this link for more details

http://www.cisco.com/univercd/cc/td/doc/product/software/ios124/124tcr/tiap_r/apl_i2ht.htm#wp1198919

4) ip ospf message-digest-key 1 md5 7 15171D091633

To enable Open Shortest Path First (OSPF) Message Digest 5 (MD5) authentication this command is used.

Usually, one key per interface is used to generate authentication information when sending packets and to authenticate incoming packets. The same key identifier on the neighbor router must have the same key value

Check this link for more details

http://www.cisco.com/univercd/cc/td/doc/product/software/ios124/124tcr/tirp_r/rteospht.htm#wp1118475

5) ip ospf cost 100

To explicitly specify the cost of sending a packet on an interface, use the ip ospf cost command in interface configuration mode.

Have a look at this link for more details

http://www.cisco.com/univercd/cc/td/doc/product/software/ios124/124tcr/tirp_r/rteospht.htm#wp1117886

6) ip ospf mtu-ignore

To disable Open Shortest Path First (OSPF) maximum transmission unit (MTU) mismatch detection on receiving Database Descriptor (DBD) packets, ip ospf mtu-ignore command is used in interface configuration mode

OSPF checks whether neighbors are using the same MTU on a common interface. This check is performed when neighbors exchange DBD packets. If the receiving MTU in the DBD packet is higher than the IP MTU configured on the incoming interface, OSPF adjacency will not be established

HTH, if yes please rate the post.

Ankur

Community Member

Re: tunnel command

Hi Ankur,

This helps a lot, thank you so much for the information...

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