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blueFast
Asked: 2014-10-03 01:02:07 +0800 CST

connect: Network is unreachable

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There are probably lots of situation when this can happen, but this is a big mistery for me. Some tools can use the network just fine (wget, dig, apt-get, ...), but some tools are just failing (ping, traceroute, the browser, ...).

For example, I can download a file with wget:

gonvaled@pegasus ~ » wget archive.ubuntu.com
--2014-10-02 10:52:34--  http://archive.ubuntu.com/
Resolving archive.ubuntu.com (archive.ubuntu.com)... 2001:67c:1360:8c01::18, 2001:67c:1360:8c01::19, 91.189.91.14, ...
Connecting to archive.ubuntu.com (archive.ubuntu.com)|2001:67c:1360:8c01::18|:80... connected.
HTTP request sent, awaiting response... 200 OK
Length: 671 [text/html]
Saving to: ‘index.html.2’

100%[========================================================================================================================================================>] 671         --.-K/s   in 0s      

2014-10-02 10:52:34 (30,8 MB/s) - ‘index.html.2’ saved [671/671]

I can resolve the domain with dig:

gonvaled@pegasus ~ » dig archive.ubuntu.com

; <<>> DiG 9.9.5-3-Ubuntu <<>> archive.ubuntu.com
;; global options: +cmd
;; Got answer:
;; ->>HEADER<<- opcode: QUERY, status: NOERROR, id: 36593
;; flags: qr rd ra ad; QUERY: 1, ANSWER: 7, AUTHORITY: 0, ADDITIONAL: 0

;; QUESTION SECTION:
;archive.ubuntu.com.        IN  A

;; ANSWER SECTION:
archive.ubuntu.com. 572 IN  A   91.189.92.200
archive.ubuntu.com. 572 IN  A   91.189.91.15
archive.ubuntu.com. 572 IN  A   91.189.91.14
archive.ubuntu.com. 572 IN  A   91.189.91.13
archive.ubuntu.com. 572 IN  A   91.189.88.153
archive.ubuntu.com. 572 IN  A   91.189.88.149
archive.ubuntu.com. 572 IN  A   91.189.92.201

;; Query time: 2 msec
;; SERVER: 10.11.0.1#53(10.11.0.1)
;; WHEN: Thu Oct 02 10:58:00 CEST 2014
;; MSG SIZE  rcvd: 148

But I can not ping the site (not because the site is not replying to pings, but because Network is unreachable):

gonvaled@pegasus ~ » ping archive.ubuntu.com
connect: Network is unreachable

Traceroute is also failing:

gonvaled@pegasus ~ » traceroute archive.ubuntu.com
traceroute to archive.ubuntu.com (91.189.88.149), 30 hops max, 60 byte packets
connect: Network is unreachable

This is my network config (nothing out of the ordinary!):

gonvaled@pegasus ~ » ifconfig eth0
eth0      Link encap:Ethernet  HWaddr 2c:76:8a:e0:b0:6b  
          inet addr:10.11.44.84  Bcast:10.11.255.255  Mask:255.255.0.0
          inet6 addr: 2001:4dd0:fff4:11:2c3f:5f86:f975:579f/64 Scope:Global
          inet6 addr: fe80::2e76:8aff:fee0:b06b/64 Scope:Link
          inet6 addr: 2001:4dd0:fff4:11:2e76:8aff:fee0:b06b/64 Scope:Global
          UP BROADCAST RUNNING MULTICAST  MTU:1500  Metric:1
          RX packets:37502 errors:0 dropped:0 overruns:0 frame:0
          TX packets:14119 errors:0 dropped:0 overruns:0 carrier:0
          collisions:0 txqueuelen:1000 
          RX bytes:13558552 (13.5 MB)  TX bytes:3533448 (3.5 MB)

gonvaled@pegasus ~ » route
Kernel IP routing table
Destination     Gateway         Genmask         Flags Metric Ref    Use Iface
10.11.0.0       *               255.255.0.0     U     0      0        0 eth0
link-local      *               255.255.0.0     U     1000   0        0 eth0

What else could I check to narrow down this issue?

EDIT

There seem to be two things at play here: IPv6 and default gateway. Whenever I enable wlan, I get these routes:

gonvaled@pegasus ~ » route
Kernel IP routing table
Destination     Gateway         Genmask         Flags Metric Ref    Use Iface
default         10.11.0.1       0.0.0.0         UG    0      0        0 wlan0
10.11.0.0       *               255.255.0.0     U     0      0        0 eth0
10.11.0.0       *               255.255.0.0     U     9      0        0 wlan0
link-local      *               255.255.0.0     U     1000   0        0 eth0

Which has a default gateway, and makes IPv4 work fine.

So now I still have two open questions:

  1. Why don't I get a default gateway with my eth0? (this is the real issue at hand)
  2. Why does IPv6 does not need a default gateway? (this is what was confusing me all along)
linux

1 Answers

  1. Best Answer

    There are two things going on:

    1) For your IPv4 settings you do not have a default route configured. It should look something like this:

    $ route  
Kernel IP routing table  
Destination     Gateway         Genmask         Flags Metric Ref    Use Iface  
default         10.11.0.0       0.0.0.0         UG    100    0        0 eth0  
10.11.0.0       *               255.255.0.0     U     0      0        0 eth0

    Since you do not have an IPv4 route specified you cannot route out of your local network.

    2) Since you are using IPv6 and IPv4 you are able to get some traffic out when you're using IPv6. If you did a route -A inet6 or ip -6 route you would most likely see a default route specified.

    • 1