Hot answers tagged

91 votes

How do I delete a route from Linux routing table

with the route -n command you'll obtain Kernel IP routing table Destination Gateway Genmask Flags Metric Ref Use Iface 0.0.0.0 192.168.178.1 0.0.0.0 UG 0 ...
47 votes

How to set the preferred network interface in Linux

Here's the complete answer, in case it helps others: To make packets with destinations 192.168.10.* use eth0, and all other packets use eth1: 1) View your current routing table ip route list One ...
  • 641
42 votes
Accepted

What makes a private IP address not routable?

Private IP addresses are routable, albeit they are not publicly routed. Basically, a router will route a private address to private/internal LAN, rather than to the internet. To expand my answer: a ...
  • 45.1k
37 votes

Multiple devices with one IPv6 to the Internet?

IPv6 is designed to not do that. Trying IPv4 style NAT with IPv6 will break things. That said, I'm pretty sure you can do NAT IPv6 with Linux iptables, so it's not impossible. But I would strongly ...
35 votes
Accepted

Is there a cloud-based reverse proxy solution in AWS?

You can use AWS API Gateway (documentation). API Gateway helps developers deliver robust, secure and scalable mobile and web application backends. API Gateway allows developers to securely connect ...
33 votes
Accepted

Does adjusting a domain name's TTL actually matter?

They're not supposed to, but some DNS services may treat this as more of a suggestion than a hard rule. They may honor the setting down to some minimum, or they may ignore your TTL completely and ...
  • 12.9k
31 votes
Accepted

Routing selection: specificity vs metric

The routes metric is to set preference among routes with equal specificity. That is true of routing in general (i.e. Cisco, Windows, etc). So the model works like: Find the most specific route (aka ...
  • 82.8k
29 votes
Accepted

Are people really going to use public IPv6 addresses on their private networks?

Is that how IPv6 is intended to work? In short, yes. One of the primary reasons for increasing the address space so drastically with IPv6 is to get rid of band-aid technologies like NAT and make ...
  • 16.6k
26 votes
Accepted

Why isn't there a route for localhost in Ubuntu?

The route command is deprecated, and should not be used anymore. The new way is to use the iproute set of commands, which are all invoked with ip followed by an object. For example: $ ip route show ...
  • 3,826
25 votes

Adding a route to specific host go out a specific interface

On a newer machine using the ip binary the syntax to add a route is slightly different (but thankfully really consistent for hosts/networks/etc). ip route add 10.0.1.3 via 10.0.0.1 dev eth0 If you ...
  • 776
23 votes

How to reload default Mac OSX routing table without rebooting

I was running into this issue while using a home OpenVPN server and connecting to it using the Tunnelblick application on Mac. What was happening on my end is that a route with my home IP as the ...
  • 331
23 votes

Why "Nexthop has invalid gateway" when it seems to be defined?

Perhaps something like: ip route add <gateway IP> dev <interface on which it should be reachable> and then ip route add default via <gateway ip> "Direct connection" can ...
21 votes

IPv6: differences between "routed prefix" and "link prefix"?

The easiest way to understand the difference between the two is via an example showing the hierarchical nature of the prefixes. An example hierarchy An ISP has been allocated a prefix from a RIR (...
  • 30.1k
21 votes

Are people really going to use public IPv6 addresses on their private networks?

We use public IPv6 addresses in our company network for all devices. We use a stateful firewall on our gateway, that: allows all icmpv6 allows new connections from internal network out allows ...
  • 1,563
21 votes

Multiple devices with one IPv6 to the Internet?

IPv6 doesn't have a NAT standard the way IPv4 does. There is an EXPERIMENMTAL RFC for one-to-one NAT (one outside address for each inside address) on IPv6, but explicitly forbids what you want to do (...
  • 3,198
19 votes

Can switches do VLAN routing?

L2 switches cannot do Inter-VLAN routing, since they only take care of L2 network stuff, that is, forward frames between links. If it is a L3 switch, then it can do IP protocol routing between VLANs.
19 votes
Accepted

IP Routing - For Office Move

When a host tries to access another host in the same subnet, it issues an ARP request for the host MAC address. If no ARP reply is received, then the host is declared unreachable. So, therefore you ...
18 votes
Accepted

How do I make actual use an IPv4 block that I own?

There are two things you need: First you need an ISP that will act as the sponsoring LIR for you. Their role is just book keeping and maintaining the contractual chain between you and RIPE NCC. Then ...
18 votes

Does adjusting a domain name's TTL actually matter?

Only if you make that change to the TTL more than three hours in advance of the IP address change. Remember that the TTL tells other DNS servers how long to cache records. So you must reduce it at ...
18 votes

How to verify a AWS VPC (S3) endpoint works?

I guess the straightfwd way is to actually probe those routes. You can traceroute to s3 and see if the NAT Gateway's internal IP is anywhere in the output (eg. the first hop). First, check the NAT ...
  • 280
17 votes

OpenVPN - how to stop public traffic routing through vpn server?

The problem was caused by Network Manager which was handling the opvn config. To disable sending all traffic through the VPN do this Click NetworkManager applet icon > VPN Connections > Configure VPN....
17 votes
Accepted

Disabling rp_filter on one interface

Info there: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux-stable.git/tree/Documentation/networking/ip-sysctl.txt?h=v4.9#n1090 Note the last sentence that would explain your attempts: ...
  • 9,496
16 votes
Accepted

MULTI: bad source address from client - any one-off solutions?

You asked: "Can someone explain why this problem occurs in the first place?" Based on what is reported in the official OpenVPN FAQ I bet it's caused by a routing problem within the OpenVPN engine. ...
16 votes
Accepted

Difference between "genmask" and "netmask"?

According to nixCraft: Genmask : The netmask for the destination net; 255.255.255.255 for a host destination and 0.0.0.0 for the default route. It's called 'genmask' because it shows the '...
15 votes

Difference beetween DNAT and REDIRECT in IPTABLES

REDIRECT does alter the destination IP address to send to the machine itself as answered by Warner@. But I'd say that answer is not totally correct, or a bit misleading. REDIRECT is not just for ...
14 votes
Accepted

Can I add a static route to a VPN network if the default gateway IP is dynamic? (Windows 7)

I've found out the answer myself: You don't actually need to specify the default gateway - you can use the catch-all of 0.0.0.0 and then specify the interface number instead (the docs do not make this ...
  • 654
14 votes

Are people really going to use public IPv6 addresses on their private networks?

If there is no need for outside connectivity, then private networks can be used. That is the reason for defining private address space also in IPv6. NAT is a hack that was invented to delay IPv4 ...
14 votes
Accepted

Use ip route add to add multicast routes to multiple interfaces

That you have multicast going through your Linux box by using unicast routing is a combination of a couple of lucky circumstances. Multicast routing is not the same as unicast routing. Unicast ...
  • 3,198
13 votes
Accepted

When to use routable vs non-routable IP addresses

Those ranges you list are described in this RFC 1918 - Address Allocation for Private Internets The title gives away their use case: "... for Private Intranets". All IP Address ranges are ...
  • 14.3k
12 votes

Why "Nexthop has invalid gateway" when it seems to be defined?

A gateway address can only be on a directly connected network. The 10.7.0.0/24 network is not directly connected to your host 10.0.0.2, but is instead separated by another network, which is connected ...

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