Duplicate first hop (but network seems fine)



  • Hi all,

    I am running pfSense 2.1 and have come across a strange situation that I would like to understand better.

    My pfSense box routes between my LAN (192.168.0.0/24) and my WAN/ISP (an Ethernet connection to a cable modem). The LAN interface is 192.168.0.250 and the WAN interface has the public IP that my ISP assigns using DHCP. The pfSense box performs NAT on traffic leaving my LAN.

    Everything seems fine, but I spotted this weirdness when running a traceroute from a box on my LAN. It is repeatable from any box on the LAN to any destination:

    traceroute to www.google.com (173.194.34.177), 30 hops max, 60 byte packets
     1  192.168.0.250  0.304 ms  0.530 ms  0.515 ms
     2  192.168.0.250  9.214 ms  10.322 ms  10.319 ms
     3  (public internet)  10.570 ms  10.563 ms  10.536 ms
    ...
    
    

    i.e. for some reason my pfSense box is showing twice, as the first and second hop. The timings suggest the packet is actually going somewhere between hop 1 and hop 2 though.

    Routing table (using 1.2.3.4 as my public WAN IP and 1.2.3.250 as ISP gateway):

    
    Destination	Gateway		Flags	Refs	Use	Mtu	Netif	Expire
    default		1.2.3.250	UGS	0	749852	1500	em0	 
    192.168.0.0/24	link#2		U	0	1400043	1500	em1	 
    192.168.0.250	link#2		UHS	0	0	16384	lo0	 
    1.2.3.0/24	link#1		U	0	32442	1500	em0	 
    1.2.3.4		link#1		UHS	0	0	16384	lo0	 
    127.0.0.1	link#6		UH	0	99	16384	lo0	 
    
    

    Has anybody seen this before? My network seems to work fine, but I would like to figure out why this looks the way it does.

    Thanks in advance for any advice.



  • A couple of days later and - without touching the pfSense box - this problem seems to have disappeared. Weird!


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