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

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31
votes
7answers
15k 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 ...
28
votes
3answers
25k 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 ...
28
votes
3answers
16k 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 ...
23
votes
2answers
63k 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 ...
18
votes
6answers
769 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
418 views

RFC 1918 address on open internet?

In trying to diagnose a failover problem with my Cisco ASA 5520 firewalls, I ran a traceroute to www.btfl.com and, much to my surprise, some of the hops came back as RFC 1918 addresses. Just to be ...
15
votes
2answers
22k 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). ...
13
votes
3answers
13k 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 ...
12
votes
1answer
201 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
765 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
1answer
348 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
701 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
253 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
14answers
30k 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 ...
9
votes
1answer
231 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 ...
9
votes
3answers
6k 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
2answers
10k 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.
8
votes
5answers
2k 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
4answers
1k 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, ...
8
votes
2answers
2k 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
4answers
13k 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 ...
8
votes
3answers
4k 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 ...
8
votes
1answer
2k 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) ...
7
votes
5answers
7k 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
596 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
1answer
12k views

What CAN cause 'RTNETLINK answers : No such process' when adding a route

I have come up against this error a number of times, but haven't yet found an explanation of what the error means, or what can cause the problem. I'm not posting my configs or the specific route I'm ...
7
votes
5answers
27k 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: ...
7
votes
2answers
527 views

Routing via Cisco ASA is changing TCP sequence/ACK numbers

Our network has a dedicated VPN appliance that sits inside the office network. We have a Cisco ASA with a static route that routes the VPN subnets to the VPN appliance. So a typical request from the ...
7
votes
2answers
6k 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
1answer
256 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
2answers
1k 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 ...
7
votes
2answers
3k 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 ...
7
votes
2answers
740 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 ...
7
votes
3answers
2k 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
12k 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 ...
6
votes
3answers
633 views

DNS servers already use anycast. Will adding more IPs enhance scalability?

RFC 1034 requires us to assign at least two IP addresses for DNS servers. However, redundancy can already be achieved by a single IP address if we use anycast addressing. BGP anycast seems to scale ...
6
votes
2answers
344 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
5answers
2k 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
1answer
446 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
2answers
295 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 ...
6
votes
5answers
7k 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 ...
6
votes
4answers
285 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
1k 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
713 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
2k 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
601 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
3answers
3k 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
5answers
3k 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
8answers
6k views

Several IP address within the same subnet on the same host

Is it possible (well the real wording should be "Is it correct") to have several IP adresses that belongs to the same subnet, on the same host ? Here is an example: #Host 1 eth0 -> 10.0.0.1/24 ...
5
votes
8answers
1k 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 ...