router's using datalink or serial protocols?
MrXpert
Member Posts: 586 ■■■□□□□□□□
in CCNA & CCENT
I've read a few sources such as dummies guide to CCENT, Trainsignal and cbt nuggets vids as well as the Cisco ICND1 book but they seem to disagree on something. I have no way of testing this to verify it as I dont have a way of analysing the protocol encapsulation between two routers.
The majority of souces i've read and watch state that If a host A wants to send a packet over to host D on another network, It will send it to its default gateway(router A).Router A then checks its routing table and works out he is connected to Router D who is the next hop router to get the packet to in order to reach host D. So router A strips off the data link mac addresses and replaces it with his own Source MAC and then router A arps(or checks his cache) for router D's MAC. Once he has this he uses the destination MAC as the one belonging to D.
In the cisco book it contradicts this and say thats between two routers they dont use MAC addresses and instead use the serial link protocol which although is also layer 2 does NOT use MAC addresses. If this is true which to be honest does sound right as mac addresses are an ethernet thing then does router A not bother arping for router D and just checks it routing table then apply a serial link encapsulation and forgets about MACs
can anyone shed some more light on this please?
The majority of souces i've read and watch state that If a host A wants to send a packet over to host D on another network, It will send it to its default gateway(router A).Router A then checks its routing table and works out he is connected to Router D who is the next hop router to get the packet to in order to reach host D. So router A strips off the data link mac addresses and replaces it with his own Source MAC and then router A arps(or checks his cache) for router D's MAC. Once he has this he uses the destination MAC as the one belonging to D.
In the cisco book it contradicts this and say thats between two routers they dont use MAC addresses and instead use the serial link protocol which although is also layer 2 does NOT use MAC addresses. If this is true which to be honest does sound right as mac addresses are an ethernet thing then does router A not bother arping for router D and just checks it routing table then apply a serial link encapsulation and forgets about MACs
can anyone shed some more light on this please?
I'm an Xpert at nothing apart from remembering useless information that nobody else cares about.
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kryolla
Member Posts: 785
I've read a few sources such as dummies guide to CCENT, Trainsignal and cbt nuggets vids as well as the Cisco ICND1 book but they seem to disagree on something. I have no way of testing this to verify it as I dont have a way of analysing the protocol encapsulation between two routers.
The majority of souces i've read and watch state that If a host A wants to send a packet over to host D on another network, It will send it to its default gateway(router A).Router A then checks its routing table and works out he is connected to Router D who is the next hop router to get the packet to in order to reach host D. So router A strips off the data link mac addresses and replaces it with his own Source MAC and then router A arps(or checks his cache) for router D's MAC. Once he has this he uses the destination MAC as the one belonging to D. this is correct but router A strips off layer 2 encapsulation upon receiving the packet and whatever is the outgoing link it will put that encapsulation when it sends the packet out
In the cisco book it contradicts this and say thats between two routers they dont use MAC addresses and instead use the serial link protocol which although is also layer 2 does NOT use MAC addresses. If this is true which to be honest does sound right as mac addresses are an ethernet thing then does router A not bother arping for router D and just checks it routing table then apply a serial link encapsulation and forgets about MACs
it doesnt really contradict it because its talking about 2 different protocols ethernet and ppp or hdlc. serieal link protocols like PPP or HDLC is a point to point protocol so there is only 2 devices on the segment, arp and inverse arp is for multipoint so its needs to know who is the other device since it can have more than 1 on the segment
can anyone shed some more light on this please?
please see my comment in boldStudying for CCIE and drinking Home Brew -
MrXpert
Member Posts: 586 ■■■□□□□□□□
thanks for clarifying this for me! I understand better. I'm an Xpert at nothing apart from remembering useless information that nobody else cares about.