Hello Eugene,
I can talk for the DSCP issue and understanding that you have: 3. Differentiated Services Field Definition A replacement header field, called the DS field, is defined, which is intended to supersede the existing definitions of the IPv4 TOS octet [RFC791] and the IPv6 Traffic Class octet [IPv6]. Six bits of the DS field are used as a codepoint (DSCP) to select the PHB a packet experiences at each node. A two-bit currently unused (CU) field is reserved and its definition and interpretation are outside the scope of this document. The value of the CU bits are ignored by differentiated services-compliant nodes when determining the per-hop behavior to apply to a received packet. http://tools.ietf.org/html/rfc2474 So basically matching that ToS value is the same as matching DSCP value of EF. ToS was the old way to do it. On that specific field the first 6 bits are reserved for DS (Differentiated Services) That is where you can define the code points and also on the ECN. Wikipedia explains it very well I guess The type of service (TOS) field in the IPv4 header has had various purposes over the years, and has been defined in different ways by five RFCs[1]. The modern redefinition of the TOS field is a six-bit differentiated services code point (DSCP) field and a two-bit Explicit Congestion Notification (ECN) field. While Differentiated Services is somewhat backwards compatible with TOS, ECN is not. http://en.wikipedia.org/wiki/Type_of_service Hope this clears a bit. From: [email protected] To: [email protected] Date: Tue, 15 May 2012 00:43:35 +0000 Subject: [OSL | CCIE_Security] DSCP values in different formats Hello folks, I ran into different ways of setting DSCP values. My two QoS relating tasks ask to match for VoIP traffic with DSCP value equals to EF. Then the verifications use something that I have no idea how to understand and cross-check with Cisco documentation. E.g. The first task verifies it with IP SLA setting the ToS to 184. The calculations of ToS value are based on the fact that the actual value of EF is 46 and then the corresponding ToS byte is 46*4=184: Ip sla 1 udp-echo 10.5.5.5 32767 source-ip 10.8.8.8 source-port 32767 control disable tos 184 timeout 1000 frequency 1 Another task uses telnet to mark all telnet traffic with DSCP value of EF by setting it right away to 0XB8. ip telnet tos B8 I understand that 0xB8 equals to 184 in decimal but what are the rules of setting DSCP in two different cases ? Is there any Cisco guide that can be used to consolidate this knowledge and access it in case of a problem during the lab ? Eugene _______________________________________________ For more information regarding industry leading CCIE Lab training, please visit www.ipexpert.com Are you a CCNP or CCIE and looking for a job? Check out www.PlatinumPlacement.com
_______________________________________________ For more information regarding industry leading CCIE Lab training, please visit www.ipexpert.com Are you a CCNP or CCIE and looking for a job? Check out www.PlatinumPlacement.com
