A Media Access Control address (MAC address) is a unique identifier assigned to network interfaces for communications on the physical network segment.

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Solaris doesn't know which MAC address to use to send an UDP multicast message

I have a pair of Solaris 10 boxes which are supposed to send multicast UDP packets to a group of hosts. One of them works just fine, whereas the other one does not. The problem with the second ...
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272 views

nmap and arp-scan inconsistent IP-MAC results

I seem to get variable and inconsistent results for the IP/MAC addresses from a particular machine, using nmap or arp-scan. The machine has 3 interfaces, and this is what it shows: $ uname -a Linux ...
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359 views

Windows Server 2008 ARP Cache Poisioning

Recently ran into a very strange problem. Several applications were having issues communication through our F5 Load-Balancer. When we looked into it we found that the router had an incorrect ARP and ...
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243 views

Redirect traffic on port 80 into apache for unknown macs, and into squid for some macs

I have a linux box behaving like a router that handles two network interfaces: eth0 for internet and eth1 for LAN. I set up iptables in order to redirect all the web traffic coming by the LAN into a ...
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1answer
28 views

Does the IP -> Ethernet multicast address mapping ambiguity matter for IGMP snooping switches?

There are 2^28 possible IP multicast addresses, but only 2^23 possible Ethernet (MAC) multicast addresses (http://technet.microsoft.com/en-us/library/cc957928.aspx), which is why e.g. 224.1.1.1 gets ...
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68 views

Possible MAC conflict in ESX

I have two virtual machines that are 10.1.1.10 and 10.1.1.20 in an ESX. I try to access theses machines by another network 192.168.1.0/24. The problem is that when I can ping one machine, I can not ...
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2k views

Ping server NETBIOS name returns wrong IP and “Destination host unreachable”

Problem server is Windows 2008 R2 VM running on VMWare ESXi 4 host. Single network adapter manually assigned single IP address (192.168.1.11). When I ping the server from any other network computer, ...
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162 views

Keepalived failover not working for Static NAT target behind Cisco ASA

I've got a Cisco ASA[0] with a pair of Linux boxes in the DMZ running Keepalived and HAproxy acting as a load-balancing failover pair for another pair of Windows servers, also in the DMZ. I'm ...
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218 views

dhcpd.conf rule-based mapping

We have ~100 physical nodes which can host a large number of VMs apiece. We need to set up dhcpd on one machine to distribute addresses in a predictable fashion based on MAC address. We'd like to go ...
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34 views

Do some network administrators assign MAC addresses with an unassigned OUI?

I am in a situation where I have observed MAC addresses on a network that do not belong to any assigned OUI range, and this is causing some issues. I suspect the cause here is a heavy use of ...
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22 views

Network access sometimes lost, disabling port security temporary solves?

I have network based primarily on Edge-Core managed switched. Port security with max mac count = 1 is enabled, DHCP snoopping enabled. Some clients have troubles with accesing network, but when I ...
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STP/RSTP: what switch should do with MAC table on a port after changing STP role of this port?

I have two switches and two active links between them. Spanning Tree Protocol is enabled on both devices, and port roles are assigned correctly: there are two Designated/Forwarding ports on RootSwitch ...
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How to detect on Linux that given MAC (HWaddr) is a virtual MAC and will change after rebooting?

Is it possible on Linux to detect automatically that given MAC (HWaddr in ifconfig output) is a virtual MAC and will change after rebooting. or alternatively is there a way to detect virtual network ...