Skip to main content

CCIE IP Precedence Vs DSCP Values

The Table bellow Represent the TOS filed in the IP Header

IPP

IPP

IPP

DropP DropP

0

ECN

ECN

Drop P = Drop Precedence IPP = IP Precedence The Drop Precedence means the probability that the packet will be dropped, the higher the value it is more likely to be dropped. IP Precedence is the importance value of a packet, the higher the value the packet is more valuable. In IP Precedence we have 0 – 7 values and you can see that by looking into the amount of fields that we have Routing (Best Effort) - 000 Priority - 001 Immediate - 010 Flash – 011 => mainly used for Voice Signaling or for Video Flash-Override - 100 Critical – 101 => mainly used for Voice RTP Internet - 110 Network - 111 You do not need to remember the name value of each one, you can simply see it with: TermServ(config)#access-list 100 permit ip any any precedence ? (0-7) Precedence value critical Match packets with critical precedence (5) flash Match packets with flash precedence (3) flash-override Match packets with flash override precedence (4) immediate Match packets with immediate precedence (2) internet Match packets with internetwork control precedence (6) network Match packets with network control precedence (7) priority Match packets with priority precedence (1) routine Match packets with routine precedence (0) with that said now we have added 2 more bits for the or more accurate 3 bits but only 2 bits we are playing with for allowing us to determine with in the scope of class witch is more preferable and for that we divided to 6 main classes Class 0 – Called also Best Effort all bits are 0 = 000000 Now we have 4 classes that are with in them divided each to 3 separate
Class1 AF11 001010 AF12 001100 AF13 001110
Class2 AF21 010010 AF22 010100 AF23 010110
Class3 AF31 011010 AF32 011100 AF33 011110
Class4 AF41 100010 AF42 100100 AF43 100110
DropP IPP Class 5 – EF Expedited Forwarding last class used for Voice Traffic Mainly 101110, and also all the DSCP values you can see with a simple ACL, but I think it is better to understand the principle and once you understand it you will not have to remember you will simply know. As it is relatively simple but the quantity makes people confused. TermServ(config)#access-list 100 permit ip any any dscp ? (0-63) Differentiated services codepoint value af11 Match packets with AF11 dscp (001010) af12 Match packets with AF12 dscp (001100) af13 Match packets with AF13 dscp (001110) af21 Match packets with AF21 dscp (010010) af22 Match packets with AF22 dscp (010100) af23 Match packets with AF23 dscp (010110) af31 Match packets with AF31 dscp (011010) af32 Match packets with AF32 dscp (011100) af33 Match packets with AF33 dscp (011110) af41 Match packets with AF41 dscp (100010) af42 Match packets with AF42 dscp (100100) af43 Match packets with AF43 dscp (100110) cs1 Match packets with CS1(precedence 1) dscp (001000) cs2 Match packets with CS2(precedence 2) dscp (010000) cs3 Match packets with CS3(precedence 3) dscp (011000) cs4 Match packets with CS4(precedence 4) dscp (100000) cs5 Match packets with CS5(precedence 5) dscp (101000) cs6 Match packets with CS6(precedence 6) dscp (110000) cs7 Match packets with CS7(precedence 7) dscp (111000) default Match packets with default dscp (000000) ef Match packets with EF dscp (101110)
Post a Comment

Popular posts from this blog

Step By Step MPLS – Basic MPLS Setup

Initial configuration , very basic with no MPLS, connectivity only to directly connected interfaces.R1R2R3R4!
!
!
interface Loopback0
ip address 1.1.1.1 255.255.255.255
!
interface FastEthernet0/0
ip address 10.0.31.1 255.255.255.0
duplex auto
speed auto
!
!
!
interface Loopback0
ip address 2.2.2.2 255.255.255.255
!
interface FastEthernet0/0
ip address 10.0.42.2 255.255.255.0
duplex auto
speed auto
!
!
!
interface Loopback0
ip address 3.3.3.3 255.255.255.255
no clns route-cache
!
interface FastEthernet0/0
ip address 10.0.31.3 255.255.255.0
duplex auto
speed auto
  no clns route-cache
!
interface Serial1/0
ip address 10.0.43.3 255.255.255.0
  serial restart-delay 0
no clns route-cache
!
!
!
interface Loopback0
ip address 4.4.4.4 255.255.255.255
no clns route-cache
!
interface FastEthernet0/0
ip address 10.0.42.4 255.255.255.0
duplex auto
speed auto
!
interface Serial1/0
ip address 10.0.43.4 255.255.255.0
  serial restart-delay 0
no clns route-cache
!
adding to the following configuration MPLS labels we will start wi…

VRF Maximum Routes

Maximum routes under customer vrf, if the service provider had unlimited resources he would not have needed that!
however normally resources are limited and expensive, and Service provider would like to make money from his available resources. maximum routes configured under VRF provide a mean of controlling PE local resource and abuse avoidance from the CE side.I have vrf called DC_EXTRANET, you can see that I have 16 routes, I have configured 10 maximum routes under that vrf however I did not want to be aggressive so I have set the warning only option. See that immediately I get a notice that I have more routes then the maximum, however no action is taken other then alerting and sending a syslog. ! PE_ashdod_otherisp.n(config-vrf)# maximum routes 10 warning-only % The current number of routes in the routing table is equal to, or exceeds the configured warning limit PE_ashdod_otherisp.n(config-vrf)# *Nov 26 20:39:41.175: %IPRT-3-ROUTELIMITWARNING: IP routing table limit warning - DC_…

ISIS Database Reading

ISIS is simple to operate normally while everything is working, most common deployments are flat network based on L2, however when there is a problem and we need to start troubleshooting then people start to get lost.So I would like to provide some tools on how to read ISIS database.notice to the “*” sign, that mean LSP was generated on the router you did the show command, you can see that host name from the show command match also host name on the LSPID,LSPID identified by hostname.xx-yy,  xx is normally 00 unless that LSP is pseudo node LSP generated by DIS , yy is representing the number of fragments for that LSP 00 – FF (max 255 fragments, plenty), most cases all the important information will be in 00 unless there are many fragments.LSP Holdtime is the amount of time an LSP will stay in database without any refresh.ATT/P/OL - 0/0/0, ATT bit or attached bit is used on L1/L2 connected to L1 node, if set to 1 L1 node will generate default route to the best L1/L2 node (best metric)AT…