{"id":1262,"date":"2018-08-14T14:41:03","date_gmt":"2018-08-14T07:41:03","guid":{"rendered":"https:\/\/lagonet.vn\/?p=1262"},"modified":"2018-08-14T14:41:03","modified_gmt":"2018-08-14T07:41:03","slug":"cisco-trace-mac-or-ip-addresses-to-switch-ports","status":"publish","type":"post","link":"https:\/\/kb.lagonet.vn\/?p=1262","title":{"rendered":"Cisco: Trace MAC or IP addresses to switch ports"},"content":{"rendered":"
\n

Cisco: Trace MAC or IP addresses to switch ports<\/h1>\n<\/header>\n
\"\"<\/div>\n
\n

Sometimes, people ask me to locate switch ports where their machines\/servers are connecting to, given that I have the MAC or IP addresses of their devices.
\nTo accomplish this task, I used to use a set of commands\u00a0show arp<\/span><\/span>,\u00a0show mac address<\/span><\/span>\u00a0 and\u00a0show cdp neighbors<\/span><\/span>\u00a0 on different switches in the network.<\/p>\n

However, I had found another way\/command which helps me to quickly get the job done. It is\u00a0traceroute\u00a0<\/span>mac<\/span><\/span><\/span>\u00a0command with two following options:<\/p>\n

    \n
  • \n
      \n
    • \n
        \n
      • traceroute mac source-MAC destination-MAC<\/li>\n
      • traceroute mac ip source-IP destination-IP<\/li>\n<\/ul>\n<\/li>\n<\/ul>\n<\/li>\n<\/ul>\n

        The command will run a\u00a0L2 trace<\/strong>\u00a0to identify a path from source address to destination address. The output of this command contains the information of the switch ports where the source and destination hosts are connecting to, and all switch-to-switch connections in between. Bear in mind that you need to run this command on L3 device.<\/p>\n

        Let me show you how it works with the network diagram above.<\/p>\n

        Note: all hosts in the network must be reachable from a L3\/Core device. I have to make sure that their IP and MAC addresses shown up when issuing the\u00a0show arp<\/span><\/span>\u00a0command<\/p>\n

        \n
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        show arp<\/span><\/p>\n

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        Python<\/span><\/p>\n<\/div>\n<\/div>\n

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        		\n
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        Core<\/span>#show arp<\/span><\/div>\n
        Protocol <\/span>Address\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0 <\/span>Age<\/span> (<\/span>min<\/span>)<\/span>\u00a0\u00a0 <\/span>Hardware <\/span>Addr\u00a0\u00a0 <\/span>Type<\/span>\u00a0\u00a0 <\/span>Interface<\/span><\/div>\n
        Internet<\/span> 192.168.100.1<\/span> \u00a0\u00a0 <\/span>–<\/span>\u00a0\u00a0 <\/span>0035.1aff.80c1<\/span> ARPA\u00a0\u00a0 <\/span>Vlan100<\/span><\/div>\n
        Internet<\/span> 192.168.100.10<\/span> \u00a0\u00a0 <\/span>2<\/span>\u00a0\u00a0 <\/span>00a0.a423.90bc<\/span> ARPA\u00a0\u00a0 <\/span>Vlan100<\/span><\/div>\n
        Internet<\/span> 192.168.100.20<\/span> \u00a0\u00a0 <\/span>3<\/span>\u00a0\u00a0 <\/span>448a.5bbc.ff61<\/span>\u00a0\u00a0<\/span>ARPA\u00a0\u00a0 <\/span>Vlan100<\/span><\/div>\n
        Internet<\/span> 192.168.200.1<\/span> \u00a0\u00a0 <\/span>–<\/span>\u00a0\u00a0 <\/span>0035.1aff.80f6<\/span> ARPA\u00a0\u00a0 <\/span>Vlan200<\/span><\/div>\n
        Internet<\/span> 192.168.200.10<\/span> \u00a0\u00a0 <\/span>3<\/span>\u00a0\u00a0 <\/span>40f2.e985.5308<\/span>\u00a0\u00a0<\/span>ARPA\u00a0\u00a0 <\/span>Vlan200<\/span><\/div>\n<\/div>\n<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n<\/div>\n<\/div>\n

        Case 1<\/strong><\/p>\n

        If I want to trace the switch ports for devices with IP addresses of\u00a0192.168.100.20 (448a.5bbc.ff61)<\/strong>\u00a0and\u00a0192.168.100.10 (00a0.a423.90bc).<\/strong>\u00a0I\u00a0use the following commands and\u00a0place the IP or MAC addresses in either source or destination addresses:<\/p>\n

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        traceroute mac ip<\/span><\/p>\n

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        Python<\/span><\/p>\n<\/div>\n<\/div>\n

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        Core<\/span>#traceroute mac ip 192.168.100.20 192.168.100.10<\/span><\/div>\n
        Translating <\/span>IP <\/span>to <\/span>mac<\/span> .<\/span>.<\/span>.<\/span>.<\/span>.<\/span><\/div>\n
        192.168.100.20<\/span> =<\/span>><\/span> 448a.5bbc.ff61<\/span><\/div>\n
        192.168.100.10<\/span> =<\/span>><\/span> 00a0.a423.90bc<\/span><\/div>\n
        <\/div>\n
        Source<\/span> 448a.5bbc.ff61<\/span> found <\/span>on <\/span>Access2<\/span><\/div>\n
        1<\/span> Access2<\/span> :<\/span> Gi0<\/span>\/<\/span>2<\/span> =<\/span>><\/span> Gi0<\/span>\/<\/span>24<\/span><\/div>\n
        2<\/span> Core<\/span> :<\/span> Gi0<\/span>\/<\/span>2<\/span> =<\/span>><\/span> Gi0<\/span>\/<\/span>1<\/span><\/div>\n
        3<\/span> Access1<\/span> :<\/span> Gi0<\/span>\/<\/span>24<\/span> =<\/span>><\/span> Gi0<\/span>\/<\/span>6<\/span><\/div>\n
        Destination<\/span> 00a0.a423.90bc<\/span> found <\/span>on <\/span>Access1<\/span><\/div>\n
        Layer<\/span> 2<\/span> trace<\/span> completed<\/span><\/div>\n<\/div>\n<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n<\/div>\n<\/div>\n
        \n
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        traceroute mac<\/span><\/p>\n

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        Core<\/span>#traceroute mac 448a.5bbc.ff61 00a0.a423.90bc<\/span><\/div>\n
        Source<\/span> 448a.5bbc.ff61<\/span> found <\/span>on <\/span>Access2<\/span><\/div>\n
        1<\/span> Access2<\/span> :<\/span> Gi0<\/span>\/<\/span>2<\/span> =<\/span>><\/span> Gi0<\/span>\/<\/span>24<\/span><\/div>\n
        2<\/span> Core<\/span> :<\/span> Gi0<\/span>\/<\/span>2<\/span> =<\/span>><\/span> Gi0<\/span>\/<\/span>1<\/span><\/div>\n
        3<\/span> Access1<\/span> :<\/span> Gi0<\/span>\/<\/span>24<\/span> =<\/span>><\/span> Gi0<\/span>\/<\/span>6<\/span><\/div>\n
        Destination<\/span> 00a0.a423.90bc<\/span> found <\/span>on <\/span>Access1<\/span><\/div>\n
        Layer<\/span> 2<\/span> trace<\/span> completed<\/span><\/div>\n<\/div>\n<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n<\/div>\n<\/div>\n

        The outputs tell me that source device (IP: 192.168.100.20 and MAC: 448a.5bbc.ff61) is on port G0\/2 of Access2 switch and the destination device (IP: 192.168.100.10 and MAC: 00a0.a423.90bc) is on port G0\/6 of Access1 switch.<\/p>\n

        Case 2<\/strong><\/p>\n

        I want to trace the switch ports for devices with IP addresses of\u00a0192.168.200.10\u00a0<\/strong>(40f2.e985.5308<\/strong>) and\u00a0192.168.100.20<\/strong>\u00a0(448a.5bbc.ff61<\/strong>). I notice that they are\u00a0NOT<\/strong>\u00a0in the same subnet\/vlan<\/strong>\u00a0(192.168.200.0\/24 vs 192.168.100.0\/24, and Vlan 200 vs Vlan 100):<\/p>\n

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        traceroute mac ip<\/span><\/p>\n

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        Python<\/span><\/p>\n<\/div>\n<\/div>\n

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        Core<\/span>#traceroute mac ip 192.168.200.10 192.168.100.20<\/span><\/div>\n
        Source <\/span>and<\/span> Destination <\/span>are <\/span>not<\/span> on <\/span>same <\/span>subnet<\/span><\/div>\n<\/div>\n<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n<\/div>\n<\/div>\n
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        traceroute mac<\/span><\/p>\n

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        Python<\/span><\/p>\n<\/div>\n<\/div>\n

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        Core<\/span>#traceroute mac 40f2.e985.5308 448a.5bbc.ff61<\/span><\/div>\n
        Error<\/span>:<\/span> Source <\/span>and<\/span> destination <\/span>macs <\/span>are <\/span>on <\/span>different <\/span>vlans<\/span>.<\/span><\/div>\n
        Layer2 <\/span>trace<\/span> aborted<\/span>.<\/span><\/div>\n<\/div>\n<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n<\/div>\n<\/div>\n

        I get nothing but error messages.
        \nAs mentioned earlier, this is a\u00a0L2 trace<\/strong>, if I use the source and destination IPs in different subnets, it will not work at all. Instead, I will get the message \u201cSource and Destination are not on same subnet\u201d, with MAC addresses, it is \u201cError: Source and destination macs are on different vlans.\u201d<\/p>\n

        To overcome this issue, I would like to pick two additional IP or MAC addresses, one in 192.168.200.0\/24 (Vlan 200) and the other in 192.168.100.0\/24 (Vlan 100), which are in the same subnets\/vlans with IP or MAC addresses above.<\/p>\n

        I can easily find them in ARP table, but it would be more convenient when I take the IP addresses of Interface Vlan 100 and 200 because they are already in my memory.<\/p>\n

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        traceroute mac ip<\/span><\/p>\n

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        Python<\/span><\/p>\n<\/div>\n<\/div>\n

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        Core<\/span>#traceroute mac ip 192.168.200.1 192.168.200.10<\/span><\/div>\n
        Translating <\/span>IP <\/span>to <\/span>mac<\/span> .<\/span>.<\/span>.<\/span>.<\/span>.<\/span><\/div>\n
        192.168.200.1<\/span> =<\/span>><\/span> 0035.1aff.80f6<\/span><\/div>\n
        192.168.200.10<\/span> =<\/span>><\/span> 40f2.e985.5308<\/span><\/div>\n
        <\/div>\n
        Source<\/span> 0035.1aff.80f6<\/span> found <\/span>on <\/span>Core<\/span><\/div>\n
        1<\/span> Core<\/span> :<\/span> Vl200<\/span> =<\/span>><\/span> Gi0<\/span>\/<\/span>2<\/span><\/div>\n
        2<\/span> Access2<\/span> :<\/span> Gi0<\/span>\/<\/span>24<\/span> =<\/span>><\/span> Gi0<\/span>\/<\/span>3<\/span><\/div>\n
        Destination<\/span> 40f2.e985.5308<\/span> found <\/span>on <\/span>Access2<\/span><\/div>\n
        Layer<\/span> 2<\/span> trace<\/span> completed<\/span><\/div>\n<\/div>\n<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n<\/div>\n<\/div>\n

        It works perfectly! The source device is Core switch (Interface Vlan 200, IP: 192.168.200.1 and MAC: 0035.1aff.80f6) and the destination device (IP: 192.168.200.10, MAC: 40f2.e985.5308) is on port G0\/3 of Access2 switch.<\/p>\n

        If you run the command and face the error massage \u201cMac found on multiple vlans\u201d, it is because the source or destination MAC address belongs to multiple VLANs, you need to indicate the VLAN where they belong to:<\/p>\n

          \n
        • \n
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            • \u00a0traceroute mac source-MAC destination-MAC vlan VLAN_ID<\/li>\n<\/ul>\n<\/li>\n<\/ul>\n<\/li>\n<\/ul>\n

              Ngu\u1ed3n:\u00a0http:\/\/netlabbuilder.net\/cisco-trace-mac-or-ip-addresses-to-switch-ports\/<\/p>\n<\/div>\n","protected":false},"excerpt":{"rendered":"

              Cisco: Trace MAC or IP addresses to switch ports Sometimes, people ask me to locate switch ports where their machines\/servers […]<\/p>\n","protected":false},"author":1,"featured_media":0,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"site-sidebar-layout":"default","site-content-layout":"","ast-site-content-layout":"","site-content-style":"default","site-sidebar-style":"default","ast-global-header-display":"","ast-banner-title-visibility":"","ast-main-header-display":"","ast-hfb-above-header-display":"","ast-hfb-below-header-display":"","ast-hfb-mobile-header-display":"","site-post-title":"","ast-breadcrumbs-content":"","ast-featured-img":"","footer-sml-layout":"","theme-transparent-header-meta":"","adv-header-id-meta":"","stick-header-meta":"","header-above-stick-meta":"","header-main-stick-meta":"","header-below-stick-meta":"","astra-migrate-meta-layouts":"default","ast-page-background-enabled":"default","ast-page-background-meta":{"desktop":{"background-color":"var(--ast-global-color-4)","background-image":"","background-repeat":"repeat","background-position":"center center","background-size":"auto","background-attachment":"scroll","background-type":"","background-media":"","overlay-type":"","overlay-color":"","overlay-opacity":"","overlay-gradient":""},"tablet":{"background-color":"","background-image":"","background-repeat":"repeat","background-position":"center center","background-size":"auto","background-attachment":"scroll","background-type":"","background-media":"","overlay-type":"","overlay-color":"","overlay-opacity":"","overlay-gradient":""},"mobile":{"background-color":"","background-image":"","background-repeat":"repeat","background-position":"center center","background-size":"auto","background-attachment":"scroll","background-type":"","background-media":"","overlay-type":"","overlay-color":"","overlay-opacity":"","overlay-gradient":""}},"ast-content-background-meta":{"desktop":{"background-color":"var(--ast-global-color-5)","background-image":"","background-repeat":"repeat","background-position":"center center","background-size":"auto","background-attachment":"scroll","background-type":"","background-media":"","overlay-type":"","overlay-color":"","overlay-opacity":"","overlay-gradient":""},"tablet":{"background-color":"var(--ast-global-color-5)","background-image":"","background-repeat":"repeat","background-position":"center center","background-size":"auto","background-attachment":"scroll","background-type":"","background-media":"","overlay-type":"","overlay-color":"","overlay-opacity":"","overlay-gradient":""},"mobile":{"background-color":"var(--ast-global-color-5)","background-image":"","background-repeat":"repeat","background-position":"center center","background-size":"auto","background-attachment":"scroll","background-type":"","background-media":"","overlay-type":"","overlay-color":"","overlay-opacity":"","overlay-gradient":""}},"footnotes":""},"categories":[33,25,16,19,6],"tags":[],"class_list":["post-1262","post","type-post","status-publish","format-standard","hentry","category-ccnp-tshoot","category-cisco","category-courses","category-issues","category-networking"],"_links":{"self":[{"href":"https:\/\/kb.lagonet.vn\/index.php?rest_route=\/wp\/v2\/posts\/1262","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/kb.lagonet.vn\/index.php?rest_route=\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/kb.lagonet.vn\/index.php?rest_route=\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/kb.lagonet.vn\/index.php?rest_route=\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"https:\/\/kb.lagonet.vn\/index.php?rest_route=%2Fwp%2Fv2%2Fcomments&post=1262"}],"version-history":[{"count":0,"href":"https:\/\/kb.lagonet.vn\/index.php?rest_route=\/wp\/v2\/posts\/1262\/revisions"}],"wp:attachment":[{"href":"https:\/\/kb.lagonet.vn\/index.php?rest_route=%2Fwp%2Fv2%2Fmedia&parent=1262"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/kb.lagonet.vn\/index.php?rest_route=%2Fwp%2Fv2%2Fcategories&post=1262"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/kb.lagonet.vn\/index.php?rest_route=%2Fwp%2Fv2%2Ftags&post=1262"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}