Am Montag, den 15.12.2008, 22:35 +0200 schrieb michel freiha: > Dear All, > I run the below tcp dump on my asterisk server > tcpdump -i eth0 -n -s0 -v udp port 5060 > I got the following result > 20:29:48.596867 IP (tos 0x10, ttl 64, id 0, offset 0, flags [DF], proto 17, > length: 373) SIP_PROXY_IP.5060 > Asterisk_IP.5060: UDP, length 345 > What i need to know please what TTL means specifically and what is the > best value og TTL and what is the lengh vale mean
Every time a TCP/IP packet travels through a router, the router substracts 1 from the TTL (time-to-live) field. The packet is discarded by the router when TTL reaches 0. This ensures a packet not to go bouncing eternally in a misconfigured routers topology. Also, is used in mesauring distances between network segments (man traceroute). Learn a bit of the commands traceroute and mtr. If you can't get any communication to very distant segments and mtr detects that, then you can play with iptables and the TTL field. otherwise, DON'T!!! The length field: the first one is the total packet size and the last is the user data contained size. Anyway, tcpdump is not very accurate in measuring UDP sizes, i mean it could make some mistakes. UDP packets travels in a connectionless environment; on the contrary, TCP establish a connection, that forces to verify that every packet reaches its destiny; udp packets are meant to be sent once and not verified. Other layers (normally layer 7, application) verify packets arrival. Good luck! -- Rodolfo Alcazar Responsable red y datos Deutsche Gesellschaft für Technische Zusammenarbeit (GTZ) GmbH Programa de Apoyo a la Gestión Pública Descentralizada y Lucha Contra La Pobreza - PADEP Av. Sánchez Lima 2226 La Paz, Bolivia Tel: +591 22417628 (121) Fax: +591 22417628 (126) Web: www.padep.org.bo Email: rodolfo.alca...@padep.org.bo _______________________________________________ -- Bandwidth and Colocation Provided by http://www.api-digital.com -- asterisk-users mailing list To UNSUBSCRIBE or update options visit: http://lists.digium.com/mailman/listinfo/asterisk-users