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Highlighted
Beginner

Serial Interface type value?

Hello,

#show adjacency Fastethernet 0/0 detail

above command displays destination MAC,source MAC and Fastethernet interface  type value:  0X800, but I wonder what is the type value for Serial interface?  and how to find out this?

Can anybody help me out in learning this ?

Regards

2 ACCEPTED SOLUTIONS

Accepted Solutions
Highlighted

Hello Suryanarayana,

I beleive that the  0x0800 mainly used for IP,  please refer to the following link for more information

http://www.cavebear.com/archive/cavebear/Ethernet/type.html

Also please find below the value when you have serial interface :

Router# show adjacency detail

Protocol Interface                 Address

IP       Serial5/0/0/1:1           point2point(7)

                                   0 packets, 0 bytes

                                   0F000800

                                   CEF   expires: 00:02:09

                                         refresh: 00:00:09

                                   Epoch: 14

IP       Serial5/0/1/1:1           point2point(7)

                                   0 packets, 0 bytes

                                   0F000800

                                   CEF   expires: 00:02:09

                                         refresh: 00:00:09

                                   Epoch: 14

Hope it will help

Ahmed Sonba

View solution in original post

Highlighted
Hall of Fame Cisco Employee

Hello,

Please allow me to join.

But my doubt is type value s for seriel interfaces are  available or not?  to identify  what type of interface just in case .. I  have never tried .. but no idea its a right question or not? sorry if I  am wrong anyway..

The type value does not identify the interface type but rather the L3 protocol carried inside a particular frame. You should not try to deduce the interface type by looking at the type value because this value is used for a different purpose - to allow the receiver to know what kind of packet is carried inside the frame.

Now, Ethernet frame format contains an EtherType field. The most common values in this field contain 0x0800 (IPv4), 0x86DD (IPv6), 0x0806 (ARP), 0x8100 (802.1Q tag), 0x8847 (MPLS).

If using Serial interfaces with Cisco HDLC frame format then the modified Cisco HDLC frame uses the EtherType field just like in Ethernet. So here is an example:

R1#show adjacency detail

Protocol Interface                 Address

IPV6     Serial1/0                 point2point(5)

                                   0 packets, 0 bytes

                                   0F0086DD

                                   IPv6 CEF   never    

                                   Epoch: 0

IP       Serial1/0                 point2point(7)

                                   0 packets, 0 bytes

                                   0F000800

                                   CEF   expires: 00:02:29

                                         refresh: 00:00:26

                                   Epoch: 0

The PPP protocol has its own "Protocol" field that describes the type of packet carried inside a PPP frame. However, the numbering is not identical with EtherType (if you are interested in knowing about PPP protocol numbers see the

http://www.iana.org/assignments/ppp-numbers/ppp-numbers.xml document). In PPP, IPv4 is 0x0021, IPv6 is 0x0057, MPLS would be 0x0281. So if I modify the Serial1/0 interface to PPP, the show adjacency output would be:

R1#show adjacency detail

Protocol Interface                 Address

IPV6     Serial1/0                 point2point(5)

                                   0 packets, 0 bytes

                                   FF030057

                                   IPv6 CEF   never    

                                   Epoch: 0

IP       Serial1/0                 point2point(9)

                                   0 packets, 0 bytes

                                   FF030021

                                   CEF   expires: 00:02:56

                                         refresh: 00:00:56

                                   Epoch: 0

Therefore, once again, this type field is not describing the type of the interface but rather the kind of L3 packet inside the particular L2 frame that can be sent out this interface.

Best regards,

Peter

View solution in original post

6 REPLIES 6
Highlighted
Beginner

Hello Suryanarayana,

Serail interface dose not have MAC address , Mac address are addresses that are relevant in  Multi-Access networks like Ethernet   In such network, you have to do an ARP broadcast to  find the MAC address of the host, so you can send packets addressed to it  and it only.

While the serial interfaces  has two ends, so it dose not need a MAC address to send  the packets.  and for that  serial interfaces doesn't have a MAC address. 

Also please refer to the following link for more information about this command

http://www.cisco.com/en/US/products/sw/iosswrel/ps5207/products_command_reference_chapter09186a0080417da1.html#wp1023146

Hope it will help

Ahmed Sonba

Highlighted

Hello Ahmed,

Thanks for your reply,

I do agree with you ... We dont need MAC address for Serial interface as encapsulation protocol will handle to send  packets.

But my doubt is type values for seriel interfaces are available or not?  to identify  what type of interface just in case .. I have never tried .. but no idea its a right question or not? sorry if I am wrong anyway..

#show adjacency Fastethernet 0/0 detail

output for this command is

protocol interface                            Address

IP       Fastethernet 0/0                 10.1.192.1 (277)

                                                      5021  packets ,  1062333 Bytes

                                                      001EF7BBF7C20019562C8FB40800

As per above output , We can easily identfy :  001EF7BBF7C2 ( Destnation MAC)

0019562C8FB4( Fastethenet 0/0 ie Source MAC Address)

and here is the area where I got doubt:

0800 is the Fastethetnet 0/0 's type value it says and identifying that this is Fastethernet

I'm bit curious to know that is there a type values for serial interfaces just incase if we may need any time to identify whether it is serial or fastethenet interface but I have never come across this... hope you understood ..any guesses..

Highlighted

Hello Suryanarayana,

I beleive that the  0x0800 mainly used for IP,  please refer to the following link for more information

http://www.cavebear.com/archive/cavebear/Ethernet/type.html

Also please find below the value when you have serial interface :

Router# show adjacency detail

Protocol Interface                 Address

IP       Serial5/0/0/1:1           point2point(7)

                                   0 packets, 0 bytes

                                   0F000800

                                   CEF   expires: 00:02:09

                                         refresh: 00:00:09

                                   Epoch: 14

IP       Serial5/0/1/1:1           point2point(7)

                                   0 packets, 0 bytes

                                   0F000800

                                   CEF   expires: 00:02:09

                                         refresh: 00:00:09

                                   Epoch: 14

Hope it will help

Ahmed Sonba

View solution in original post

Highlighted

Thanks Ahmed,

Sounds like there is no type values for Serial interfaces...However, Thank you so much for the research.

Highlighted
Hall of Fame Cisco Employee

Hello,

Please allow me to join.

But my doubt is type value s for seriel interfaces are  available or not?  to identify  what type of interface just in case .. I  have never tried .. but no idea its a right question or not? sorry if I  am wrong anyway..

The type value does not identify the interface type but rather the L3 protocol carried inside a particular frame. You should not try to deduce the interface type by looking at the type value because this value is used for a different purpose - to allow the receiver to know what kind of packet is carried inside the frame.

Now, Ethernet frame format contains an EtherType field. The most common values in this field contain 0x0800 (IPv4), 0x86DD (IPv6), 0x0806 (ARP), 0x8100 (802.1Q tag), 0x8847 (MPLS).

If using Serial interfaces with Cisco HDLC frame format then the modified Cisco HDLC frame uses the EtherType field just like in Ethernet. So here is an example:

R1#show adjacency detail

Protocol Interface                 Address

IPV6     Serial1/0                 point2point(5)

                                   0 packets, 0 bytes

                                   0F0086DD

                                   IPv6 CEF   never    

                                   Epoch: 0

IP       Serial1/0                 point2point(7)

                                   0 packets, 0 bytes

                                   0F000800

                                   CEF   expires: 00:02:29

                                         refresh: 00:00:26

                                   Epoch: 0

The PPP protocol has its own "Protocol" field that describes the type of packet carried inside a PPP frame. However, the numbering is not identical with EtherType (if you are interested in knowing about PPP protocol numbers see the

http://www.iana.org/assignments/ppp-numbers/ppp-numbers.xml document). In PPP, IPv4 is 0x0021, IPv6 is 0x0057, MPLS would be 0x0281. So if I modify the Serial1/0 interface to PPP, the show adjacency output would be:

R1#show adjacency detail

Protocol Interface                 Address

IPV6     Serial1/0                 point2point(5)

                                   0 packets, 0 bytes

                                   FF030057

                                   IPv6 CEF   never    

                                   Epoch: 0

IP       Serial1/0                 point2point(9)

                                   0 packets, 0 bytes

                                   FF030021

                                   CEF   expires: 00:02:56

                                         refresh: 00:00:56

                                   Epoch: 0

Therefore, once again, this type field is not describing the type of the interface but rather the kind of L3 packet inside the particular L2 frame that can be sent out this interface.

Best regards,

Peter

View solution in original post

Highlighted

Wow!! Awesome!!!

Yes, Absolutely , after looking at Mr.Ahmed output I did confused and had lot of research on why 0800 is there for type value even for serial interface and then came to the conclusion that, " This value represents the Ethernet type field,which indicates that the frame containing an IP packet,because Ethernet type value 0x800 is registered as the value for IP".

But you have given the right and exact information:

"Therefore, once again, this type field is not describing the type of the  interface but rather the kind of L3 packet inside the particular L2  frame that can be sent out this interface."

... Thanks a lot. At atleast, have some satishfaction that I have learned some thing new today.... hope this helps others too..

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