the process by which data packets on communication networks are forwarded into the direction of their ultimate destination by routers.
26
votes
3answers
13k views
Tuning Linux IP routing parameters — secret_interval and tcp_mem
We had a little failover problem with one of our HAProxy VMs today. When we dug into it, we found this:
Jan 26 07:41:45 haproxy2 kernel: [226818.070059] __ratelimit: 10 callbacks suppressed
Jan 26 ...
20
votes
8answers
7k views
What is “anycast” and how is it helpful?
I'd never heard of anycast until a few seconds ago when I read this SF post.
The wikipedia entry on it is quite formal and doesn't really evoke a mental picture of how it would be used.
Can someone ...
18
votes
6answers
733 views
Why do Facebook users sometimes end up on my site when they enter www.facebook.com in their browser?
Every few weeks I get an email (usually a very unpleasant one) or sometimes even a phone call from a Facebook user who believes that I am "hacking" their internet. They come to this conclusion after ...
15
votes
2answers
12k views
What is the difference between unicast, anycast, broadcast and multicast traffic?
I have never had the privilege of working in an environment that required complicated routing or if it did require it, it was handled upstream of me. I've always used very simple static routing ...
14
votes
2answers
30k views
Can I have multiple DHCP servers on one network?
This is a Canonical Question about Redundant DHCP Servers.
Is it possible to have more than one DHCP server on the same LAN? What are the implications of doing this?
What happens if there is ...
12
votes
1answer
189 views
What's the point of SAN routing?
I'm familiar with extending fabrics by adding more switches to it, but i don't get why sometimes it's better to do routing between fabrics (considering all the switches are from the same vendor, using ...
11
votes
3answers
10k views
How is route automatic metric calculated on Windows 7?
KB299540 explains how Windows XP automatically assign metrics to IP routes:
The following table outlines the criteria that is used to assign metrics for routes that are bound to network interfaces ...
11
votes
3answers
301 views
Use Windows DHCP/DHCPv6 server without setting a static address
You cannot set the Windows DHCP/DHCPv6 server to listen on dynamic addresses or all addresses, only static addresses. Is there a technical reason for this limitation? Is there any workaround?
My ...
10
votes
2answers
13k views
How to reload default Mac OSX routing table without rebooting
Greetings,
I'm using vpnc for a VPN client. I'm also doing some tricky things with route to make sure I can still access my local network, etc. etc. (the particulars here are not very important).
...
10
votes
1answer
279 views
Network Restructure Method for Double-NAT network
Due to a series of poor network design decisions (mostly) made many years ago in order to save a few bucks here and there, I have a network that is decidedly sub-optimally architected. I'm looking for ...
10
votes
3answers
522 views
No internet after dhcp lease renews
Today we had a number of machines stop getting internet access. After a lot of troubleshooting, the common thread is that they all had their dhcp lease renewed today (we're on 8 day leases here).
...
10
votes
2answers
193 views
Traffic routing with unreliable connections
I have a group of offices that are all connected to the main office via DSL links on the far end to save costs. (We're a non-profit, don't ask)
We've historically had noticeable problems with the ...
9
votes
3answers
5k views
Windows Server 2008 - Connecting to 127.0.0.1
Im running Windows Server 2008 R2, we have an application that connects from (binds to) a public IP on the server to 127.0.0.1:8334 [connects to a service listening on 0.0.0.0:8334]
In Windows 2003, ...
8
votes
14answers
23k views
How to securly join two networks together over the Internet?
Let's say there are two locations. Both locations have their own fast Internet connections.
How do you join these two networks together such that every computer can see every other computer?
Do you ...
8
votes
5answers
1k views
Traceroute includes un-routable IP (?)
I ran the following traceroute once, while trying to disagnose a network problem.
c:\>tracert linode.com -d
Tracing route to linode.com [67.18.186.61]
over a maximum of 30 hops:
1 <1 ms ...
8
votes
2answers
1k views
Redundant OpenVPN connections with advanced Linux routing over an unreliable network
I am currently living in a country that blocks many websites and has unreliable network connections to the outside world. I have two OpenVPN endpoints (say: vpn1 and vpn2) on Linux servers that I use ...
8
votes
1answer
856 views
CentOS, two nics eth0 eth1 with different subnets aren't reachable outside VLAN/subnet
I am having an issue with a CentOS 6.3 box.
We have two NICs (eth0 and eth1) in the server which each have an ip from a different subnet assigned, let's say eth0:192.168.1.2/24 (gateway 192.168.1.1) ...
8
votes
1answer
200 views
Where can I embed proprietary information in a layer 2 or layer 3 packet?
The Citrix Netscaler has an interesting property that embeds information in the TCP packet that gets sent to the host. This property is echoed back to the Netscaler in such a way that the Netscaler ...
7
votes
4answers
959 views
Multi-WAN bonding across different media
I've recently been thinking again about a product that Viprinet
provide, basically they've got a pair of routers, one that lives in a
datacentre, Their VPN Multichannel Hub and the on-site hardware, ...
7
votes
5answers
6k views
Routing protocols, distance vector vs link state
I'm trying to figure out the differences(pros/cons) between two routing protocols approach and I would be great-full for any help, advice and explanation. As far I can say that it seems like distance ...
7
votes
2answers
389 views
Architecting your network when you run out of VLANs
This is an entirely hypothetical question, I'm not in this situation now.
What happens to your VLAN topology and routing if you run a multi tenant network and you have more than 4096 customers?
Do ...
7
votes
2answers
6k views
How to permanently redirect port 80 to 8080 on OS X?
On OS X 10.6 you do not have iptables, so what is the full solution for this permanently redirect all request sent to port 80 to another port, like 8080?
It has to be persistent.
7
votes
2answers
743 views
Is it possible to include switches in traceroute hops?
I was wondering if it's at all possible to make a Dell Powerconnect 2848 switch show when running internal traceroutes. This would help with diagnosing issues and make it far easier to see where ...
7
votes
2answers
2k views
Why do ICMP Redirect Host happen?
I'm setting up a Debian box as a router for 4 subnets. For that I have defined 4 virtual interfaces on the NIC where the LAN is connected (eth1).
eth1 Link encap:Ethernet HWaddr ...
7
votes
3answers
7k views
Windows static routes w/o specifying gateway (next hop)
I have the following scenario:
Computer A: 198.51.100.8, netmask 255.255.255.0
Computer B: 203.0.113.9, netmask 255.255.255.0
Both computers are on the same LAN segment; no default gateway is ...
7
votes
1answer
221 views
OpenVPN Client timing out
I recently installed OpenVPN on my Ubuntu VPS. Whenenver I try to connect to it, I can establish a connection just fine.
However, everything I try to connect to times out.
If I try to ping ...
7
votes
3answers
1k views
OpenVPN client without redirect-gateway doing triangular routing and IP spoofing not working on Ubuntu
I have an OpenVPN client running on a server of mine obtaining a public IP on a remote network in a different country. The client configuration is as follows:
dev tap
remote a.b.30.7
float a.b.30.7
...
6
votes
2answers
276 views
When an IP or a block of IPs are assigned to you, do the network admins just add them to a router?
Let's say there is a router to the internet and a router separates your network from others within a data center.
When the data center provided gives you IP addresses, do they just take a [set] of ...
6
votes
1answer
362 views
2 ethernet connections between two Switches
I'm setting up servers at our new office and I brought a spare managed switch with 2 Gig ports to run all of our phones(VOIP) and workstations.
Now for the servers I've got a separate gigabit ...
6
votes
4answers
910 views
Private IP getting routed over Internet
We are setting up an internal program, on an internal server that uses the private 172.30.x.x subnet... when we ping the address 172.30.138.2, it routes across the internet:
C:\>tracert ...
6
votes
4answers
269 views
Why don't we see more routing attacks?
So, who remembers the whole "Pakistan kills YouTube" debacle from February last year? Here's an article on the topic to refresh your memory:
Insecure routing redirects YouTube to Pakistan
The gist ...
6
votes
8answers
922 views
opvnvpn: addressing nodes in LAN-behinds
I've setup an openvpn server which i can access remotely, once it is connected, it creates a tun0 device on both server and client with virtual ip 10.15.119.x. the openvpn server is itself ...
6
votes
1answer
399 views
If I change a router's subnet mask to one that includes the old one, will the hosts with the old configuration still work?
Currently I have a router that is addressed as 10.2.1.1 on a 10.2.1.0/24 network. All of my hosts have default gateway 10.2.1.1 with mask 255.255.255.0.
I want to know: if I change my router to ...
6
votes
3answers
1k views
Amazon CloudFront and EC2: Global Load Balancing
We have an app that is going to store and serve up a decent amount of data in S3 to a global audience where latency should be minimized. So, we've been doing tests with Amazon CloudFront and have seen ...
6
votes
2answers
2k views
Openvpn for client/server in same subnet
I'm trying to openvpn into an office network (192.168.1.0/24) from a client sitting on a network with the same subnet (also 192.168.1.0/24). It is a linux (ubuntu 9.10) server and windows client.
I ...
6
votes
2answers
370 views
Per-user routing doesn't seem to work
So, I'm trying to implement per-user routing so that I'm able to route all btpd torrent traffic over a VPN. Unfortunately, btpd does not currently allow you to bind to a specific IP address. :(
I ...
6
votes
2answers
549 views
Linux Router Problem
I have a Linux based router with four interfaces (each with its own private subnet).
When I directly connect a device directly (i.e. no switch, just a patch cable) to one interface and another device ...
6
votes
3answers
2k views
Border firewalls and routing — static vs dynamic routing
Let's say you've got an enterprise with a small internet presence in the form of a DNS server, a web server, and a VPN server, all on the DMZ (in this case, an invisible pair of switches connected ...
5
votes
2answers
8k views
Where route to 169.254.0.0 comes from?
Running CentOS 5.4
Why do I have route to 169.254.0.0 although it does not appear in Network > Ethernet Device > Route configuration dialog?
Destination Gateway Genmask Flags ...
5
votes
5answers
2k views
Hubs/switches taking out switches?
Here's the issue...we have a network with a lot of Cisco switches.
Someone plugged in a hub on the network, and then we started seeing "weird" behavior; errors in communication between clients and ...
5
votes
2answers
240 views
When to start using OSPF
We have 4 offices in different countries. They are all connected via VPN to each other (i.e. at least one VPN tunnel from each office to all other three). Each office has between 1 and 4 separate ...
5
votes
8answers
960 views
Help putting together a server for Routing/Firewall/VPN purposes
we're currently in the process of putting together our own server Firewall/Router. We were going to use a dedicated solution from someone like Juniper or Watchguard, but it is going to be a lot more ...
5
votes
5answers
5k views
Is it possible to connect a single NIC to two different VLANs?
I know it is possible to assign multiple IP addresses to the same NIC as long as they are on the same sub-net (e.g. server A can be assigned both 192.168.1.1 and 192.168.1.2).
However, is it possible ...
5
votes
2answers
802 views
IP Routing - how does it work again?
Can someone explain how IP routing works to me?
E.g. if i ping 123.123.123.123, how does each router know which way to go as shown in a trace route dump.
5
votes
6answers
17k views
Ping “replies” from same computer with 'Destination host unreachable' (no route to other computer)
I've got two computers in a LAN behind a wireless router.
One has XP with ip 192.168.1.2
This one has W7 with ip 192.168.1.7
If I try to ping the other one from this computer, I get this:
...
5
votes
2answers
2k views
/etc/interfaces file for multiple gateways, same network? (linux)
I've got my ip routing table setup as I'd like it:
# ip r s
10.1.248.0/24 dev eth0 proto kernel scope link src 10.1.248.11
default via 10.1.248.1 dev eth0 metric 100
default via 10.1.248.3 dev ...
5
votes
3answers
545 views
Round Robin Default Gateways on Linux
Does Linux have native support for load balanced (maybe as simple as RR or IP Hash) multiple default gateways?
5
votes
2answers
204 views
Do I need routing protocols on a small network?
I have a small network with 10 VLANs, mostly routed via our core layer 3 switch. RIP is enabled on the core switch, but I'm in the process of adding a second router for a couple of VLANs as our core ...
5
votes
3answers
2k views
Why does ifconfig reset the default gateway route?
In FreeBSD, an ifconfig call seems to delete the default gateway route, even when given the same IP-address (e.g. when updating the netmask only). Is it a bug or a feature?
As fas as I remember Linux ...
5
votes
2answers
682 views
linux routing bug?
I have been struggling with this not easily reproducible issue since a while. I am using linux kernel v3.1.0, and sometimes routing to a few IP addresses does not work.
What seems to happen is that ...
