Problem

Can't reach Guest OS from Host OS via network, while all other network connections (Guest OS and Host OS to external addresses) works perfectly.

This problem might occur if the ARP cache is corrupted either on the Host system or on a network switch.

Solution

Verify that both Host and Guest OS are able to ping anywhere internally and externally; that static or DHCP is correct, and that DNS name resolution works without issue.

If the packets transmitted from Host to Guest and Guest to Host are not reaching the gateway, the root cause is the ARP cache not keeping up with the changes made by CHARON.

Clear the ARP cache to resolve the issue.

• To clear the ARP cache on the switch, please refer to the switch's documentation
  
  
• To clear the ARP cache on Windows:
  • Remove CHARON NDIS driver
  • Flush the cache:

    • Open the command line (cmd.exe) using run as administrator
      Use the arp -a command to display all your ARP entries

      ...> arp -a

      .

    • Use the following command to flush the entire cache:

      ..> netsh interface ip delete arpcache

      .

    • Refer to the following article if needed: Quick Tips: Flush the ARP cache in Windows 7  (credits: www.techrepublic.com)
  • Reinstall CHARON NDIS driver
  • Run NCC to configure NICs dedicated to CHARON
    
    
• To clear the ARP cache on Linux, you can proceed one of two ways:

  • Clearing the cache with the arp command: using "arp -n" (or arp) to list the ARP cache and arp -d to flush out entries

    # arp -d 192.168.1.1 # arp -n Address                  HWtype  HWaddress          Flags Mask            Iface 192.168.1.1                      (incomplete)                             eth0 192.168.1.2             ether   00:02:9b:a2:d3:f3   C                     eth0 192.168.1.3             ether   00:02:9b:d9:d1:a2   C                     eth0

    .

  • Clearing the cache with the ip command: newer Linux distributions have the ip utility, which has a more advanced way to clear out the full ARP cache

    # ip -s -s neigh flush all 192.168.1.1 dev eth0 lladdr 00:a1:04:c6:10:14 used 757/757/28 probes 6 STALE 192.168.1.2 dev eth0 lladdr 00:02:9b:a2:d3:f3 used 2555/719/659 probes 6 STALE 192.168.1.3 dev eth0 lladdr 00:02:9b:d9:d1:a2 ref 1 used 0/0/0 probes 6 DELAY *** Round 1, deleting 3 entries *** *** Flush is complete after 1 round ***

    The first -s will provide a more verbose output. The second -s defines the neighbor table, which equals the ARP and NDISC cache.

    .

  • Please refer to the following article if needed: How to clear the ARP cache on Linux? (credits: www.linux-audit.com )

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