Oct 28 2008
Simplified NSAP format
The actual NSAP format is quite complicated. Luckily there is a simplifed format which is used in most implementations.
Click here to view a power point show on the simplified NSAP format.
Oct 28 2008
ISIS adjacencies
IS-IS adjacencies
Point-to-point adjacencies are formed in a slightly differnet manner than those on broadcast links. Therefore different types of IS-IS hello packets are used. The three different types of IS-IS
hello packets are:-
Point-to-point hello
Level 1 LAN hello
Level 2 LAN hello
As specified in ISO 10589, the TLVs used in Point-to-point hellos are limited to the following:-
Area Addresses (Type 1 )
Padding (Type 8 )
Authentication Type (Type 10 )
Point-to-Point adjacencies
On a Point-to-point link IS-IS hellos are sent periodicaly every 10 seconds (hello interval) to maintain the adjacency.
Below is a list of header fields sent in Point-to-point hellos.
Circuit Type – Level 1, Level 1-2 or Level 2 only
Source ID – System ID of the router that generated the hello packet
Holding Time – Maximum interval between two consecutive hello packets before the router is considered no longer available
PDU Length – Length of the entire PDU, including header
Local Circuit ID – Unique link identifier
TLV Fields – Variable-length fields.
TLV 240 enhances the IS-IS Point-to-Point adjacency setup process by introduing the concept of a three way handshake by confirming the presence of its SysID in a TLV 240 attached to hellos received from its neighbor.
LAN adjacancies
Similar to OSPF, IS-IS over a multi-access network involved the use of a psuedonode. Nodes on the LAN send their hellos to well-known Level 1 and Level 2 broadcast MAC addresses.
Below is a list of header fields sent in LAN level 1 and 2 hellos.
Circuit Type – Tells whether this circuit is Level 1-only, Level 2-only, or both.
Source ID – The SysID of the originator
Holding Time – Maximum interval between two consecutive hello packets before the router is considered no longer available
PDU length – Length of the entire PDU, including header
Priority – This 7 bit value designates the priority to be the DIS on the LAN.
LAN ID – SysID of the DIS plus an octet-long unique ID for this router assigned by the DIS.
The broadcast addresses for the Level 1 and Level 2 hellos is as follows:-
01-80-C2-00-00-15 for Level 2 adjacencies (AllL2ISs)
01-80-C2-00-00-14 for Level 1 adjacencies (AllL1ISs)
Oct 27 2008
Introduction into IS-IS
Ok, here are some introductory points on ISIS. ISIS is a manual cost link state protocol. ISIS was designed within the ConnectionLess Network Service framework(CLNS). CLNS is supported by the following ISO protocols.
- CLNP – ISO 8473
- ES-IS – ISO 9542
- IS-IS – ISO 10589
CLNP, ES-IS and IS-IS all operate at layer 3 of the 7 layer OSI model. They are differentiated by the value of the initial protocol identifier field in the first octet. As you can see from this ISIS packet capture*, the “Intra Domain Routing Protocol Discriminator” is set to 0×83. The list below shows the value of the Routing Protocol Discriminator in the first octet of their encoded protocl formats for CLNP, ES-IS and IS-IS.
- CLNP: 0×81 (10000001)
- ES-IS: 0×82 (10000010)
- IS-IS: 0×83 (10000011)
IS-IS packets
There are three types of IS-IS packets. Hello packets, Link-state packets and sequence number packets.
Hello packets are used to establish adjacencies between IS-IS neighbors.
Link-state packets are used to distribute routing information between IS-IS nodes.
Sequence number packets are used to control distribution of Link-state packets ie sequence number packets provide a method of synchronisation of the link state databases in an IS-IS routing area.
There are 3 subcatagories of Hello packets: Level 1, level 2 and Point-to-point hello. There are 2 subcatagories of Link-state packets: Level 1 and Level 2. There are 4 subcatagories of sequence number packets: Level 1 and 2 complete sequence number packets and Level 1 and 2 partial sequence number packets
From this packet capture* you can see a Point-to-point hello, layer 1 and 2 link state packet, complete and partial sequence number packet.
*packet capture taken from http://packetlife.net/captures/protocol/isis/
Oct 25 2008
ISIS header
Below is a diagram of the ISIS header. The different ISIS packets ie hellos and SNPs have slightly different headers, however the first 8 bytes are identical.
Click here to see a power point show on the isis header.
Oct 25 2008
MPLS Header
This is what an MPLS label looks like. The MPLS label contains a 20-bit label, dont get confused between the different uses of the word label.
The 3 bit EXP bits are used for QoS purposes. You can use them to define different tunnel modes, which I’ll talk about on another day.
The S bit identifies the bottom label of the stack.
The TTL field is similar to the IP TTL, ie if the MPLs TTL reaches zero the MPLS frame is discarded.
The MPLS frame is inserted between the layer 2 frame header and the layer 3 header.
Click here if you want to see a powerpoint version of the MPLS frame header
Oct 25 2008
IP Packet Header
Below is a diagram of the IPv4 header. The header is 20bytes long in most cases, however this can be extendend using the options field.
Click here to see a power point version of the header.
Oct 23 2008
CCIE SP Training schedule
Here is the CCIE SP schedule which I will be working from. Im sure there will be some slippage, thats life.
If you want to join in the program feel free, there is a linkedin group called CCIE Service Provider. Feel free to join.
Anyway here is the program.
# IGP Routing 26th oct-8th nov
1. IS-IS, Level 1/2, Metric
2. OSPF, LSA, Area
3. Redistribution, Summarization, Filtering
4. Policy routing
# MPLS 9th nov -22 nov
1. Label distribution, LDP/ TDP
2. Label filtering, Label merging, Multipath
3. MPLS COS
4. MPLS Netflow
5. MPLS over ATM
6. MPLS Traffic Engineering
# L3/L2 VPN 23rd nov – 6th dec
1. MPLS VPN, MP-iBGP
2. PE-CE routing, RIPv2, OSPF, EIGRP, Static, ISIS, EBGP
3. BGP Extended Community
4. Inter AS MPLS VPN
5. Carrier Supporting Carrier
6. VRF-Lite, VRF Select
7. Multicast MPLS VPN
8. GRE, multipoint GRE
9. AToM, L2TPv3
10. 802.QinQ
# SP Multicast 7th dec – 20 dec
1. PIM-SM, PIM-DM, SSM, PIM-BIDIR, IGMP
2. Auto RP, Static RP, BSR, Anycast RP
3. MP-BGP for multicast, MSDP
# High Availability 21st dec – 3 Jan
1. NSF, GLBP
2. Fast reroute, Link/Node protection
3. HSRP, VRRP
# Bridging and Switching 4th Jan – 17th Jan
1. VTP, VLAN, Trunk, Spanning tree
2. Frame Relay, DLCI, FR multilink
3. ATM PVC, SVC, FR/ATM interworking
4. PPPoE
# EGP Routing 18th Jan – 31st Jan
1. IBGP, EBGP
2. BGP attributes
3. Confederation, Route reflector
4. Synchronization, Aggregation, Stability
5. Redistribution, Filtering
6. Multipath
# SP QoS and Security 1st Feb – 14th feb
1. DSCP/EXP, TOS, NBAR
2. Marking, Shaping, Policing
3. CAR, FRTS
4. WRQ, CBWFQ, LLQ, PQ, CQ
5. RED, WRED
6. LFI, cRTP
7. RSVP
8. ACL, RPF, Filtering
9. Routing update security
10. Common attacks
# Management 15th feb – 28th feb
1. SNMP, SYSLOG, RMON
2. Accounting
3. Netflow
4. NTP
# CCIE Lab – 30th feb – 15th March
if pass — Sleep for 2 weeks
if fail — cry lots then try again.
good luck