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Internet Protocol, Transport Control Protocol, Network protocols, Routing, Routers, IP aliases, Routes, Ethernet

 [ Total topics 58 Go to page 1, 2, 3, 4, 5, 6

Message
 Post subject: icmp port unreachable error message
PostPosted: Mon Jul 08, 2013 5:44 am 
Hello,

I am sending UDP packets from one PC to another. I am watching the the whole activity using Wire Shark. I notice that for some time there is smooth transmission of packets from one system to the other. Then suddenly ICMP packets with error 'port unreachable' starts to appear. Then they disappear for some time and there is again smooth transmission of UDP packets. Then these ICMP packets again appear with the same 'port ...

Read more : icmp port unreachable error message | Views : 1772 | Replies : 4

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 Post subject: icmp port unreachable error message
PostPosted: Mon Jul 08, 2013 5:43 am 
Hello,

I am sending UDP packets from one PC to another. I am watching the the whole activity using Wire Shark. I notice that for some time there is smooth transmission of packets from one system to the other. Then suddenly ICMP packets with error 'port unreachable' starts to appear. Then they disappear for some time and there is again smooth transmission of UDP packets. Then these ICMP packets again appear with the same 'port ...

Read more : icmp port unreachable error message | Views : 899 | Replies : 0

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 Post subject: Quagga: Exiting: failed to connect to any daemons.
PostPosted: Mon Jul 01, 2013 4:44 pm 
Quagga can fail with following error due to pid directory permission errors:
Code:
# /etc/init.d/quagga restart                                   
Stopping Quagga daemons (prio:0): (ospfd) (zebra) (bgpd) (ripd) (ripngd) (ospf6d) (isisd).
Removing all routes made by zebra.
Loading capability module if not yet done.
Starting Quagga daemons (prio:10): zebra ospfd.
Exiting: failed to connect to any daemons.

# strace /usr/lib/quagga/ospfd -- --daemon -A 127.0.0.1
...
fstat(4, {st_mode=S_IFREG|0444, st_size=0, ...}) = 0
mmap(NULL, 4096, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANONYMOUS, -1, 0) = ...

Read more : Quagga: Exiting: failed to connect to any daemons. | Views : 4504 | Replies : 0

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 Post subject: FreeBSD tcpdump on enc0 doesn't show any traffic
PostPosted: Fri Jun 21, 2013 8:54 am 
FreeBSD supports enc0 pseudo interface (kernel "device enc") that is used for ipsec tunnels. The external interface will show encrypted traffic and enc0 interface will show unencrypted traffic.

If tcpdump doesn't show any packets on enc0 interface, that is most probably because it is not up. Example:

Code:
[root@host]# ifconfig enc0
enc0: flags=0<> metric 0 mtu 1536
        nd6 options=29<PERFORMNUD,IFDISABLED,AUTO_LINKLOCAL>



Bring up the interface and you will start seeing packets with tcpdump:
[root@host]# ifconfig enc0 up
[root@host]# ...

Read more : FreeBSD tcpdump on enc0 doesn't show any traffic | Views : 2071 | Replies : 0

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 Post subject: TCP - Duplicate segment
PostPosted: Mon Dec 31, 2012 12:41 am 
hi,
i want to know that, when tcp sends a (due to delayed ack) duplicate segment which is already received by the receiver, what the receiver should do...
whether it will discard the old segment and send the ack or, new segment will be discarded..

Read more : TCP - Duplicate segment | Views : 633 | Replies : 0

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 Post subject: TCP first packet loss
PostPosted: Wed Dec 12, 2012 4:44 am 
hi,
i am implementing tcp per rfc 793, i have one doubt, in tcp while sending the first packet, lost means, the sender should wait and retransmit the first segment again or, it should send the second packet,

please answer, if you know

Read more : TCP first packet loss | Views : 685 | Replies : 0

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 Post subject: TCP first packet loss
PostPosted: Wed Dec 12, 2012 1:43 am 
hi,
i am implementing tcp per rfc 793, i have one doubt, that if tcp sent the 1st packet, but that is lost, now whether tcp should send second packet or, after retransmit the 1st packet and get the ack, the second pakcet should send.

if you know, please help me...

Read more : TCP first packet loss | Views : 825 | Replies : 1

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 Post subject: How to block ping icmp echo requests without a firewall in Linux
PostPosted: Mon Nov 26, 2012 9:46 am 
To stop all icmp echo-request packets in Linux without enabling a firewall use the following sysctl:
Code:
# sysctl net.ipv4.icmp_echo_ignore_all=1
net.ipv4.icmp_echo_ignore_all = 1


To check:
Code:
# tcpdump -nni eth0 icmp

Read more : How to block ping icmp echo requests without a firewall in Linux | Views : 1287 | Replies : 0

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 Post subject: FreeBSD em driver overwrites incoming vlan tagged frames 802.1p priority field
PostPosted: Wed Nov 21, 2012 10:59 am 
# ifconfig em0
em0: flags=8843<UP,BROADCAST,RUNNING,SIMPLEX,MULTICAST> metric 0 mtu 1500
options=20db<RXCSUM,TXCSUM,VLAN_MTU,VLAN_HWTAGGING,POLLING,VLAN_HWCSUM,WOL_MAGIC>
ether 00:07:e9:a5:9b:fa
media: Ethernet autoselect (1000baseTX <full-duplex>)
status: active
# tcpdump -nni em0 -ve -l | grep --color ', p '
tcpdump: WARNING: em0: no IPv4 address assigned
tcpdump: listening on em0, link-type EN10MB (Ethernet), capture size 65535 bytes
15:51:50.654610 00:07:e9:a5:9b:fa > 2c:21:72:c6:c1:88, ethertype 802.1Q (0x8100), length 190: vlan 10, p 0, ethertype IPv4, (tos 0x10, ttl 64, id 22972, offset 0, flags [DF], proto ...

Read more : FreeBSD em driver overwrites incoming vlan tagged frames 802.1p priority field | Views : 1938 | Replies : 0

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 Post subject: Tcpdump: How to capture first two packets of tcp conversation (SYN/SYN+ACK)
PostPosted: Wed Jun 13, 2012 5:32 am 
Capturing only SYN (fist packet) of tcp conversation:
Code:
$ sudo tcpdump -nni eth0 port 80 and tcp[13] == 2

09:26:23.044132 IP 181.210.53.36.24495 > 10.0.0.2.80: Flags [S], seq 4179562228, win 65535, options [mss 1280,nop,wscale 3,nop,nop,TS val 290512683 ecr 0,sackOK,eol], length 0


How to capture only SYN packet with tcpdump:


Code:
$ sudo tcpdump -nni eth0 port 80 and "tcp[13] == 2"

Capturing both SYN and SYN+ACK (fist two packet) of tcp conversation with tcpdump:


...

Read more : Tcpdump: How to capture first two packets of tcp conversation (SYN/SYN+ACK) | Views : 19609 | Replies : 0

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 [ Total topics 58 Go to page 1, 2, 3, 4, 5, 6


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