Query on operstatus for link, can I change it?
Hi, I am looking for a way to change the operstatus shown for the network interface. Problem: I have an extra interface on the machine that I would like to use for some program like tcpreplay and tcpdump/wireshark. So, I would like to play a pcap file on this interface and then capture on the same interface with wireshark. Now the problem with this is that unless a cable is plugged in I do not see any packets in wireshark, although I do not see any failures in sending the packets. I would like to do this without any cable being plugged in as I do not intend to send the packets out, is this possible? The reason I cannot use lo interface for doing this is: there will be other packets on the lo interface and I want to capture only the packets in the pcap file that I am playing with tcpreplay. Thanks in advance for any advice on this. -- Thanks, -aka ___ Kernelnewbies mailing list Kernelnewbies@kernelnewbies.org http://lists.kernelnewbies.org/mailman/listinfo/kernelnewbies
RE: Query on operstatus for link, can I change it?
-Original Message- From: kernelnewbies-boun...@kernelnewbies.org [mailto:kernelnewbies- boun...@kernelnewbies.org] On Behalf Of Amit Agarwal Sent: Tuesday, July 14, 2015 5:14 AM To: Kernelnewbies Subject: Query on operstatus for link, can I change it? Hi, I am looking for a way to change the operstatus shown for the network interface. Problem: I have an extra interface on the machine that I would like to use for some program like tcpreplay and tcpdump/wireshark. So, I would like to play a pcap file on this interface and then capture on the same interface with wireshark. Now the problem with this is that unless a cable is plugged in I do not see any packets in wireshark, although I do not see any failures in sending the packets. I would like to do this without any cable being plugged in as I do not intend to send the packets out, is this possible? The reason I cannot use lo interface for doing this is: there will be other packets on the lo interface and I want to capture only the packets in the pcap file that I am playing with tcpreplay. Thanks in advance for any advice on this. -- Thanks, -aka You might be able to make something like this work using network namespaces and veth devices. Depends on whether you really need to use your extra physical interface as the tcpreplay device. Jeff Haran ___ Kernelnewbies mailing list Kernelnewbies@kernelnewbies.org http://lists.kernelnewbies.org/mailman/listinfo/kernelnewbies
RE: Query on operstatus for link, can I change it?
-Original Message- From: kernelnewbies-bounces+jharan=bytemobile@kernelnewbies.org [mailto:kernelnewbies- bounces+jharan=bytemobile@kernelnewbies.org] On Behalf Of Amit Agarwal Sent: Tuesday, July 14, 2015 12:54 PM To: Kernelnewbies Subject: Re: Query on operstatus for link, can I change it? ... One last query on this, does this interface receive any packet by default of any protocol. I think of the two virtual interfaces as real NICs with a cable between them. I am pretty sure they are protocol agnostic. If so, how do I make sure that no packets other than one injected by me are seen on this interface. Sorry, if this sounds too stupid, but I am noob in this area. That's what routing tables are for. 8^) Jeff Haran ___ Kernelnewbies mailing list Kernelnewbies@kernelnewbies.org http://lists.kernelnewbies.org/mailman/listinfo/kernelnewbies
Re: Query on operstatus for link, can I change it?
On 15-07-14 20:38:49, Jeff Haran wrote: -Original Message- I think of the two virtual interfaces as real NICs with a cable between them. I am pretty sure they are protocol agnostic. Yes, pretty much that. If so, how do I make sure that no packets other than one injected by me are seen on this interface. Sorry, if this sounds too stupid, but I am noob in this area. That's what routing tables are for. 8^) right :) Thanks a ton Jeff. With your advice and some google, I think I can settle for dummy interface which is similar to veth - only difference being it creates one interface. Commands remain the same and I have to change only veth to dummy for type in the ip command. Also I found that I can set netmask to /32, turn off multicast and arp which should get me to what I wanted. Thanks again. -- Thanks, -aka Beware of Programmers who carry screwdrivers. -- Leonard Brandwein ___ Kernelnewbies mailing list Kernelnewbies@kernelnewbies.org http://lists.kernelnewbies.org/mailman/listinfo/kernelnewbies
Re: Query on operstatus for link, can I change it?
On 15-07-14 19:34:42, Jeff Haran wrote: The last time I looked into this (and this was quite a while ago so take this with much salt) the lo device was not a regular network device. The stack sets up an instance of lo in every network name space created, more or less automatically via the registration of its init routine in a struct pernet_operations. So lo doesn't initialize like most other network devices. You might have issues there. I know I did last time I tried to borrow loopback.c to do something similar for some prototyping I was doing. Realized that while looking at this code. But thankd for pointing this. If you are willing to monkey with kernel code, it might be easier to just twiddle the link sense routine in driver for the other NIC you were planning to use to always report the link as up regardless of what the PHY says. This too is good option. Found anther option that looks like should solve the problem I am after. veth device - as you suggested earlier. So, as I understand veth device creates a sender and receiver. So, if I send on veth0, I will receive on veth1. So, the steps that I would need is (using iproute2 utility): ip link add type veth name veth0 peer name veth1 ip link set dev veth0 up ip link set dev veth1 up and then add the address to what ever I require. I quickly tested and seems that I am able to play on veth0 and receive on veth1. One last query on this, does this interface receive any packet by default of any protocol. If so, how do I make sure that no packets other than one injected by me are seen on this interface. Sorry, if this sounds too stupid, but I am noob in this area. -- Thanks, -aka ___ Kernelnewbies mailing list Kernelnewbies@kernelnewbies.org http://lists.kernelnewbies.org/mailman/listinfo/kernelnewbies
Re: Query on operstatus for link, can I change it?
Hi Jeff, On 15-07-14 16:06:39, Jeff Haran wrote: -Original Message- You might be able to make something like this work using network namespaces and veth devices. Depends on whether you really need to use your extra physical interface as the tcpreplay device. Thanks for this pointer. I will check if I can achieve what I want with netns. Also, I was wondering if I can just copy the loopback.c file, build it as module and do insmod after changing the network name from lo to something else, will that work? -- Thanks, -aka ___ Kernelnewbies mailing list Kernelnewbies@kernelnewbies.org http://lists.kernelnewbies.org/mailman/listinfo/kernelnewbies
