the process by which data packets on communication networks are forwarded into the direction of their ultimate destination by routers.

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55
votes
8answers
50k views

What is “anycast” and how is it helpful?

I'd never heard of anycast until a few seconds ago when I read "What are some cool or useful server/networking tricks?". The wikipedia "Anycast" article on it is quite formal and doesn't really evoke ...
46
votes
2answers
154k 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 more ...
14
votes
4answers
43k views

iptables - Target to route packet to specific interface?

My home server has two main interfaces, eth1 (a standard internet connection) and tun0 (an OpenVPN tunnel). I'd like to use iptables to force all packets generated by a local process owned by UID ...
8
votes
4answers
3k 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, ...
60
votes
3answers
100k 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 ...
30
votes
3answers
20k 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 ...
5
votes
2answers
7k views

Can't ping multihomed Linux machine on non-default interface

I have a multihomed Ubuntu server with a set of interfaces that includes: eth2: 10.10.0.131/24 eth3: 10.20.0.2/24 The default interface is eth2, with a gateway of 10.10.0.1. Here's what the routing ...
4
votes
2answers
831 views

IPv6: differences between “routed prefix” and “link prefix”?

What are the exact differences between "routed prefix" and "link prefix" for IPv6?How do these differences in a wireshark-Trace? (if you observe a Host with an assigned "routed prefix" or a Host with ...
2
votes
2answers
15k views

Routing decision when there are two default gateways on windows

My windows machine has two network cards, both have default gateways. How does windows determine which gateway should it access when sending a packet to a remote endpoint? More precisely, here's my ...
5
votes
2answers
4k views

Routing selection: specificity vs metric

I understand that Linux chooses the most specific route to the destination when it does routing selection. But what about a route's metric? Does it have a higher priority than route's specificity? A ...
3
votes
1answer
3k views

OS X 10.8: redirecting locally initiated ssh connections to localhost:22

I need to hack the OS X pf to redirect all ssh connections from an user to this machine. I want, when doing $ ssh google.com to get the same results as with $ ssh localhost ie a connection to ...
2
votes
1answer
5k views

How to configure routing between Azure virtual networks?

I'm designing an Azure environment which will contain multiple virtual networks, and a requirement is for all networks to be connected; a VM in any network should be able to talk to another VM in any ...
5
votes
4answers
2k views

Prevent SSH connection lost after logging into VPN on server machine

I encountered an issue that I can't deal with. When I'm logged onto an VPS over SSH and try to estabilish VPN connection on that VPS, the SSH connection between VPS and my machine get lost. I assume ...
3
votes
1answer
13k views

OpenVPN server cannot ping clients

I have OpenVPN set up on a Debian server. Clients can connect, and clients can ping and access resources (Samba shares and intranet) on the server. However, the server cannot ping the client - it ...
2
votes
2answers
2k views

Change source address based on destination IP

We have several "router" machines that gather a lot of external IP addresses on the same host and redirect, NAT or proxy the traffic to the internal network. They also act as routers for the machines ...
0
votes
1answer
635 views

Configure routes in OpenVPN

I am trying to figure out how to setup routing on OpenVPN. I have successful connection between client (OS X Snow Leopard) and server (OS X Leopard Server), and each can ping the other. However, I am ...
5
votes
10answers
14k views

Forward port to another Ip/port

I recently found out that my ISP disables port 135. I have a server and personal computer behind my router. A friend and I are working on a programming project and are running into some sql issues ...
2
votes
2answers
1k views

BGP Multihomed/Multi-location best practice

We're in the process of designing a new iteration of our network where we improve resilliency by adding a second datacentre. We'll be adding a second datacentre, with an identical configuration of ...
1
vote
1answer
523 views

why port forwarding is not working in this setup?

I'm trying to setup a docker virtualization environment. This is a follow up of this question. I have a virtual eth0:0 interface, and I would like to forward it using iptables. The public, main IP ...
0
votes
1answer
3k views

Cisco ASA 5505 Voice/Data VLANs not pinging/routing

Hi i am very new to Cisco ASA 5000 series and have two interfaces that i would like to route between, a data network 192.168.69.0/24 and voice 192.168.70.0/24, I have addded both and can ping the ...
17
votes
5answers
113k views

How to route different traffic thru different network interfaces (in Windows)

I've searched for details on how to do this but I've been unsuccessful - I wondered if someone could offer up some advice. So, let's say I have 2 network cards (LAN and 3G in my instance), both ...
14
votes
2answers
27k 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 ...
10
votes
1answer
64k views

Two network interfaces and two IP addresses on the same subnet in Linux

I recently ran into a situation where I needed two IP addresses on the same subnet assigned to one Linux host so that we could run two SSL/TLS sites. My first approach was to use IP aliasing, e.g. ...
16
votes
4answers
22k 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 ...
4
votes
2answers
525 views

Linux TC / Policy Routing tools

In addition to a really good firewall Linux has a builtin advanced routing and traffic shaping (lartc). There are many applications (firehol, firestarter, etc) to make the creation of iptables ...
8
votes
2answers
8k views

ip address scope parameter

In Linux, the command ip address add [...] has a scope argument. The man page says that the scope is "the scope of the area where this address is valid". Follows the list of legal scopes: global ...
0
votes
1answer
8k views

Using DD-WRT to connect to VPN and Forward all traffic of certain devices through VPN

I have been able to setup my dd-wrt router to connect to an openvpn server and route all traffic through the vpn to the internet. This makes it so all traffic comming in from the LAN to the ...
9
votes
1answer
14k views

Difference beetween DNAT and REDIRECT in IPTABLES

Okay, it may be because I am dense or maybe just not finding the right source, but I can't understand why one of these IPTABLES setups would be better than the other. Here is my setup: I have a box ...
8
votes
4answers
15k views

second ip address on the same interface but on a different subnet

Is it possible in CentOS 5.7 64bit to have a second IP address on one interface (eg. eth0) - alias interface configuration - in a different subnet? Here is the original config for eth0 more etc/...
3
votes
3answers
2k views

Recommend- XORP vs GNU Zebra vs Quagga [closed]

Any recommendations which of XORP, GNU Zebra and Quagga routing software is simple enough to hack and learn?
2
votes
2answers
6k views

Permanently adding source policy routing rules

Somebody answered my earlier question by describing how to create a new routing table with source policy routing: echo 13 eth3 >> /etc/iproute2/rt_tables ip route add default via 10.20.0.1 ...
1
vote
2answers
3k views

OSPF: how to advertise the subnet of an OpenVPN server?

I have successfully configured OSPF on all of our HP ProCurve 7102 routers, and most of our internal Linux routers. Routes get advertised, and all is peachy. Except for the routes into the subnets ...
6
votes
2answers
11k views

Debian/OVH: How to configure multiple Failover IP on the same Xen (Debian) Virtual Machine?

I have a problem on a Xen virtual machine (running latest Debian), when I try to configure a second failover IP address. OVH reports that my IP is misconfigured and they complaint they receive a ...
6
votes
5answers
12k views

Specifing ip address for outbound connections on a multi ip host

one of my servers (Debian 5.0.6) has two public ip-address on the same interface. This used to work well for months but suddenly it is using "the wrong" ip addresses for outgoing connections. This is ...
5
votes
2answers
2k views

Policy based routing

I found very good article on load balancing at http://www.diegolima.org/wordpress/?p=36.. I could not implement it though as my requirement is slightly different from pure load balancing. We have two ...
4
votes
3answers
8k views

How to configure remote access to multiple subnets behind a SonicWALL NSA 2400

I have a client that uses a SonicWALL NSA 2400 as their firewall. I need to setup a second LAN subnet for a handful of PC. Management has decided that there should be a second subnet even though ...
4
votes
2answers
2k views

IP Routing - how does it work again? [closed]

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 traceroute dump.
3
votes
1answer
5k views

Is it possible to configure HAProxy to choose a backend server based on a request's source IP? If so, how?

The title pretty much says it all. Basically, I want to route a request to a specific backend server based on the request's source IP. i.e., HTTP Request from 192.168.100.1 -> HAProxy -> ...
3
votes
1answer
13k views

How to set up routing for RRAS VPN connections

I have a NAT/firewall running DHCP for the LAN configured to forward the VPN ports directly to the Windows 2008R2 server behind the firewall on NIC1. The LAN switch is also connected to the firewall ...
2
votes
2answers
2k views

How to change routing for skype packets?

I can't seem to find a way to somehow change routing for Skype packets. I have following situation: host ha, in lan, runs skype. host ha has gateway "gw1" gw1 has 2 separate network connections - ...
2
votes
2answers
5k views

Specifying a preferred route when there are multiple links to same network

I have a server with multiple interfaces and IP addresses on the same network. I would like for non-iSCSI traffic to exclusively use one of the interfaces, and for iSCSI traffic to exclusively use the ...
2
votes
2answers
4k views

How do you prevent a VPN from exposing your IP when it disconnects?

I want every connection in a Virtual Machine (windows XP) to ONLY use my OpenVPN server, as soon as the connection is lost to OpenVPN, I want to lose all internet connectivity in the VM. Naturally the ...
2
votes
1answer
5k views

How do I setup routing for two companies with different Internet connections on the same LAN?

Here's the setup: Two companies (A & B) share office space and a LAN. A 2nd ISP is brought in and company A wants its own Internet connection (ISP A) and company B wants its own Internet ...
2
votes
2answers
4k views

Redirecting to other internal servers based on sub domain

Here is my situation home network, windows machines, 1 external facing IP address (that allows port 80) 1 windows home server always on machine, planning on upgrading to WHS 2011 soon. several IP ...
1
vote
3answers
2k views

VM routing in a dedicated ESXi server

I'm trying to set up a dedicated server with an ESXi installed on it: I was given 2 blocks of public IPs Block A. 1IP = X.X.X.204, used in ESXi vmkernel port IP (and gateway pointing to X.X.X.1)...
1
vote
1answer
1k views

Is there any way to filter packets (eg. by iptables) after routing is complete?

I want to drop certain packet destined to an ip_address AFTER it has reached the POSTROUTING chain. However, for iptables, the "nat" table cannot be used for filtering so the following doesn't work: ...
1
vote
2answers
7k views

Get linux to change default route if one path goes down?

I'm configuring a gateway/router linux box. It is performing masquerading/NAT. The primary Internet interface is a 3G modem, but if that goes down, I would like it to try a different interface ...
-2
votes
1answer
11k views

PPTP IPTables routing issue

PPTP connects just fine to the radius server PPTP modules are loaded into the kernel PPTP connects fine to the pptp service Question: How do I get the PPTP to connect to the internet? IPTables: #!...
9
votes
1answer
2k views

Aws vpc default route table in CloudFormation

Am I missing something but is there no way to add a route via CloudFormation to the default route table that comes provisioned with a VPC?
8
votes
1answer
6k 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) ...