Re: DHCP client can't connect to a web site

[Mark Buchanan <mabuchan@gmail.com>]

This may not be the ultimate problem, but traceroute on windows and Linux sometimes use different protocols.   On Linux and UNIX systems, many times they use UDP, but if memory is correct Windows uses an ICMP traceroute.  This could explain why Linux Traceroute fails, but Windows works, if the destination host is blocking UDP.   Maybe this has changed over time, as my memory of these two is going back 10+ years.

That doesn’t explain why one works and the other doesn’t.  But may be a single factor in some of the diagnosis.

Another item could be that the TTL of the Linux system is too small, Granted I believe it’s typically a minimum of 64.  I experienced this issue in the mid 90s when we hooked the colleges systems to the internet and a pair of systems had a TTL of 16.  

Lastly I know from working in an ISP, that sometimes the ingress for network bandwidth and the egress are different providers, which may have differing TTLs.   So there may be some weirdness with anything TTL related depending on how touting is being implemented.

Just a few thoughts.   :)

--
Mark Buchanan

> On Mar 17, 2018, at 16:23, dsavage@peaknet.net wrote:
> 
> The setup:
> 
> AT&T U-verse (new router) with internal DHCP and 3-bit IPv4 (five user
> fixed IP addresses) network.
> 
> Windows 10 PC on copper Ethernet assigned to one of those fixed IP addresses.
> 
> CentOS 7.4 laptop on WiFi issued a non-routable DHCP address.
> 
> The problem:
> 
> The DHCP WiFi laptop cannot connect to slashdot.org (216.34.181.45). DNS
> resolution works fine, but traceroute to the name and IP address both fail
> after 30 hops.
> 
> The fixed IP Windows PC connects perfectly.
> 
> How can this be?
> 
> --Doc Savage
>  Fairview  Heights,  IL
> 
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