Re: Mac address for Serial Ports?? [7:31898]
Serial interfaces don't have MAC addresses. IPX is a special case because the network-layer node address IS the MAC address. Think about frame formats and identifications for WAN protocols. What identifies the sender in Frame Relay? A DLCI. How about ATM? A VPI/VCI pair. How about PPP? No need because it's point-to-point. How about HDLC. No need because it's point-to-point (in Cisco HDLC anyway). How does a network layer address get mapped to a data-link identifier? Static mapping or Inverse ARP for some protocols. PPP has the NCP which sits between the two layers. Priscilla At 02:51 PM 1/14/02, Cisco Nuts wrote: >Hello, >Is there a way of verifying that a serial port in borrowing the mac address >of the Ethernet/Tr port when it is connecting to another router in an IP >network? >I see this in an ipx network but not in an ip network. sh ipx int s0 > >I tried the debug ip packet, detail, debug arp, debug broadcast etc. but I >am not seeing that the serial port is using a mac address. > >What test can I do on my router to check that the serial port does borrow >the first available Mac address of a Ethernet port on a router? > >Thank you. > >_ >Join the worlds largest e-mail service with MSN Hotmail. >http://www.hotmail.com Priscilla Oppenheimer http://www.priscilla.com Message Posted at: http://www.groupstudy.com/form/read.php?f=7&i=31904&t=31898 -- FAQ, list archives, and subscription info: http://www.groupstudy.com/list/cisco.html Report misconduct and Nondisclosure violations to [EMAIL PROTECTED]
Re: Mac address for Serial Ports?? [7:31898]
At 10:50 PM 1/14/02, Cisco Nuts wrote: >Sorry Priscilla but I am trying to understand, IP does not need a mac >address to get to the next hop( on a point-to-point netw - PPP or HDLC)!! >Why? Because it is a point-to-point as you say? But I thought ip was layer >three. It is Layer 3, but in most cases to send an IP packet requires a Layer 2 address also. But not if there's only one possible recipient, the other end of the point-to-point link. I'm not sure I understand your confusion, but maybe this will help. Compare IP on a LAN to IP on a WAN. For example, assume you have configured IP addresses on some Ethernet stations and also on some router serial interfaces and you're doing some pinging. A LAN device sends an ARP packet to find the MAC address that maps to the destination IP address. On a point-to-point WAN, a device doesn't do this. It assumes there's only one place the packet can go -- to the other end. Also compare this to Frame Relay and ATM. In this case, a device learns in advance through Inverse ARP which data-link identifier to use when sending to an IP address. Maybe the point is just too obvious or you haven't thought about the fact that a point-to-point link is a special case Please send questions to the group. I like to answer to the group so that everyone benefits from the answer and any discussion that follows. Priscilla >I understand in terms of ATM or FR but ip on a point-to-point? >Am I missing something here? >Sorry, can you help? > > >>From: "Priscilla Oppenheimer" >>Reply-To: "Priscilla Oppenheimer" >>To: [EMAIL PROTECTED] >>Subject: Re: Mac address for Serial Ports?? [7:31898] >>Date: Mon, 14 Jan 2002 15:37:15 -0500 >> >>Serial interfaces don't have MAC addresses. IPX is a special case because >>the network-layer node address IS the MAC address. >> >>Think about frame formats and identifications for WAN protocols. What >>identifies the sender in Frame Relay? A DLCI. How about ATM? A VPI/VCI >>pair. How about PPP? No need because it's point-to-point. How about HDLC. >>No need because it's point-to-point (in Cisco HDLC anyway). >> >>How does a network layer address get mapped to a data-link identifier? >>Static mapping or Inverse ARP for some protocols. PPP has the NCP which >>sits between the two layers. >> >>Priscilla >> >>At 02:51 PM 1/14/02, Cisco Nuts wrote: >> >Hello, >> >Is there a way of verifying that a serial port in borrowing the mac address >> >of the Ethernet/Tr port when it is connecting to another router in an IP >> >network? >> >I see this in an ipx network but not in an ip network. sh ipx int s0 >> > >> >I tried the debug ip packet, detail, debug arp, debug broadcast etc. but I >> >am not seeing that the serial port is using a mac address. >> > >> >What test can I do on my router to check that the serial port does borrow >> >the first available Mac address of a Ethernet port on a router? >> > >> >Thank you. >> > >> >_ >> >Join the worlds largest e-mail service with MSN Hotmail. >> >http://www.hotmail.com >> >> >>Priscilla Oppenheimer >>http://www.priscilla.com >_ >Get your FREE download of MSN Explorer at http://explorer.msn.com/intl.asp. > Priscilla Oppenheimer http://www.priscilla.com Message Posted at: http://www.groupstudy.com/form/read.php?f=7&i=31919&t=31898 -- FAQ, list archives, and subscription info: http://www.groupstudy.com/list/cisco.html Report misconduct and Nondisclosure violations to [EMAIL PROTECTED]
Re: Mac address for Serial Ports?? [7:31898]
Thank you very much. Yes, I do understand now. Regards. >From: "Priscilla Oppenheimer" >Reply-To: "Priscilla Oppenheimer" >To: [EMAIL PROTECTED] >Subject: Re: Mac address for Serial Ports?? [7:31898] >Date: Mon, 14 Jan 2002 18:33:24 -0500 > >At 10:50 PM 1/14/02, Cisco Nuts wrote: > >Sorry Priscilla but I am trying to understand, IP does not need a mac > >address to get to the next hop( on a point-to-point netw - PPP or HDLC)!! > >Why? Because it is a point-to-point as you say? But I thought ip was >layer > >three. > >It is Layer 3, but in most cases to send an IP packet requires a Layer 2 >address also. But not if there's only one possible recipient, the other end >of the point-to-point link. > >I'm not sure I understand your confusion, but maybe this will help. Compare >IP on a LAN to IP on a WAN. For example, assume you have configured IP >addresses on some Ethernet stations and also on some router serial >interfaces and you're doing some pinging. > >A LAN device sends an ARP packet to find the MAC address that maps to the >destination IP address. On a point-to-point WAN, a device doesn't do this. >It assumes there's only one place the packet can go -- to the other end. > >Also compare this to Frame Relay and ATM. In this case, a device learns in >advance through Inverse ARP which data-link identifier to use when sending >to an IP address. > >Maybe the point is just too obvious or you haven't thought about the fact >that a point-to-point link is a special case > >Please send questions to the group. I like to answer to the group so that >everyone benefits from the answer and any discussion that follows. > >Priscilla > > > >I understand in terms of ATM or FR but ip on a point-to-point? > >Am I missing something here? > >Sorry, can you help? > > > > > >>From: "Priscilla Oppenheimer" > >>Reply-To: "Priscilla Oppenheimer" > >>To: [EMAIL PROTECTED] > >>Subject: Re: Mac address for Serial Ports?? [7:31898] > >>Date: Mon, 14 Jan 2002 15:37:15 -0500 > >> > >>Serial interfaces don't have MAC addresses. IPX is a special case >because > >>the network-layer node address IS the MAC address. > >> > >>Think about frame formats and identifications for WAN protocols. What > >>identifies the sender in Frame Relay? A DLCI. How about ATM? A VPI/VCI > >>pair. How about PPP? No need because it's point-to-point. How about >HDLC. > >>No need because it's point-to-point (in Cisco HDLC anyway). > >> > >>How does a network layer address get mapped to a data-link identifier? > >>Static mapping or Inverse ARP for some protocols. PPP has the NCP which > >>sits between the two layers. > >> > >>Priscilla > >> > >>At 02:51 PM 1/14/02, Cisco Nuts wrote: > >> >Hello, > >> >Is there a way of verifying that a serial port in borrowing the mac >address > >> >of the Ethernet/Tr port when it is connecting to another router in an >IP > >> >network? > >> >I see this in an ipx network but not in an ip network. sh ipx int s0 > >> > > >> >I tried the debug ip packet, detail, debug arp, debug broadcast etc. >but >I > >> >am not seeing that the serial port is using a mac address. > >> > > >> >What test can I do on my router to check that the serial port does >borrow > >> >the first available Mac address of a Ethernet port on a router? > >> > > >> >Thank you. > >> > > >> >_ > >> >Join the worlds largest e-mail service with MSN Hotmail. > >> >http://www.hotmail.com > >> > >> > >>Priscilla Oppenheimer > >>http://www.priscilla.com > >_ > >Get your FREE download of MSN Explorer at >http://explorer.msn.com/intl.asp. > > > > > > >Priscilla Oppenheimer >http://www.priscilla.com _ Get your FREE download of MSN Explorer at http://explorer.msn.com/intl.asp. Message Posted at: http://www.groupstudy.com/form/read.php?f=7&i=31922&t=31898 -- FAQ, list archives, and subscription info: http://www.groupstudy.com/list/cisco.html Report misconduct and Nondisclosure violations to [EMAIL PROTECTED]
