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EIGRP

EIGRP. Enhanced Interior Gateway Protocol. OSPF vs EIGRP. EIGRP Metric calculation . Default constant values:- K1=1, K2=0, K3=1, K4=0, K5=0 Metric = [K1 x bandwidth (min) + K3 x delay (cumulative)].

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EIGRP

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  1. EIGRP Enhanced Interior Gateway Protocol

  2. OSPF vs EIGRP

  3. EIGRP Metric calculation • Default constant values:- K1=1, K2=0, K3=1, K4=0, K5=0 • Metric = [K1 x bandwidth (min) + K3 x delay (cumulative)] Metric = 256*([K1*Bw + K2*Bw/(256-Load) + K3*Delay]*[K5/(Reliability + K4)]). The default K values can be changed with the EIGRP router command: R2(config-router)# metric weights tos k1 k2 k3 k4 k5

  4. R2 R3 R1 Bandwidth Metric Calculation 172.16.2.0/24 Loopback 10.1.1.1/30 ISP .1 S0/0/0 S0/0/1 DCE 172.16.3.0/24 192.168.10.8/30 .2 .9 S0/0/0 DCE S0/0/1 64 kbps 1024 kbps Fa0/0 .10 .1 Fa0/0 S0/0/1 172.16.1.0/24 1544 kbps 192.168.1.0/24 S0/0/0 DCE .1 .1 .5 .6 192.168.10.4/30 Bandwidth = (10,000,000 / BW in kbps) x 256 • R2 Slowest Interface = S0/0/1 link at 1024kbps • 10,000,000 / 1024 = 9765.625 • Round Down = 9765 • 9765 x 256 =2,499,840

  5. R2 R3 R1 Delay Metric Calculation 172.16.2.0/24 Loopback 10.1.1.1/30 ISP .1 S0/0/0 S0/0/1 DCE 172.16.3.0/24 192.168.10.8/30 .2 .9 S0/0/0 DCE S0/0/1 64 kbps 1024 kbps Fa0/0 .10 .1 Fa0/0 S0/0/1 172.16.1.0/24 1544 kbps 192.168.1.0/24 S0/0/0 DCE .1 .1 .5 .6 192.168.10.4/30 Delay = (Sum of delay / 10) x 256 • Sum = 100 + 20,000 = 20,100uS • Sum /10 = 20,100 / 10 = 2,010 • 2,010 x 256 = 514,560

  6. R2 R3 R1 Composite Metric Calculation 172.16.2.0/24 Loopback 10.1.1.1/30 ISP .1 S0/0/0 S0/0/1 DCE 172.16.3.0/24 192.168.10.8/30 .2 .9 S0/0/0 DCE S0/0/1 64 kbps 1024 kbps Fa0/0 .10 .1 Fa0/0 S0/0/1 172.16.1.0/24 1544 kbps 192.168.1.0/24 S0/0/0 DCE .1 .1 .5 .6 192.168.10.4/30 Calculate the metric to reach destination 192.168.1.0/24 from R1 Metric = [K1 x bandwidth (min) + K3 x delay (cumulative)]

  7. R3 R5 R4 R2 R1 Convergence -The Diffusing Update Algorithm (DUAL) • The feasibility condition (FC) is met when a neighbor's reported distance (RD) to a network (192.168.10.0/24) is less than the local router's feasible distance (FD) to the same destination network. 10 20 10 25 10 10 30 45 FC = RD<FD 15 10 192.168.10.0/24 • Successor = R2 (FD=20) • Feasible Successor = R3 (10<20) 15 30

  8. Convergence - The Diffusing Update Algorithm (DUAL) R3 R5 R4 R2 R1 • If the Successor route fails, R1 will immediately enter the feasible successor into the routing table. • R1 will update it’s neighbours about the topology change. 10 20 10 25 10 10 30 45 Update ACK FC = RD<FD 15 10 192.168.10.0/24 Update • Successor = R3 (FD=25) • No Feasible Successor = R3 (30>25) 15 30 ACK

  9. Convergence/Fault Tolerance - The Diffusing Update Algorithm (DUAL) R3 R5 R4 R2 R1 • If the new successor route fails, R1 no longer has a feasible successor, so it enters the Active state. • R1 will now query it’s neighbours for a route to network 192.168.10.0/24. 10 20 10 25 10 30 45 FC = RD<FD 15 10 192.168.10.0/24 Query • Successor = R4 (FD=45) • No Feasible Successor 15 30 Reply

  10. Equal Cost Load Balancing • Equal-cost load balancing is the ability of a router to distribute traffic over all its network ports that are the same metric from the destination address. • EIGRP automatically load balances across equal cost paths. Load balancing increases the use of network segments and increases effective network bandwidth. • Cisco IOS software by default will install up to four equal-cost paths in the routing table for most routing protocols. • The maximum-paths command in can be used to allow up to six equal-cost paths.

  11. Equal Cost Load Balancing R3 R5 R4 R2 R1 • EIGRP can also balance traffic across multiple routes that have different metrics, which is called unequal-cost load balancing. • The degree to which EIGRP performs load balancing is controlled with the variance command 10 20 10 25 10 10 30 45 FC = RD<FD 15 10 192.168.10.0/24 R1(config)#router eigrp 1 R1(config-router)#variance 2 15 30

  12. Unequal Cost Load Balancing-Routing Loops • How will R1 route packets to R2’s loopback interface? • Issues if R1 uses both direct path and and indirect path using R3? Routing Loops Unequal cost paths

  13. Not Designed to Transit Traffic Scalability – Limiting Queries: Hub & Spoke Network Hub Network • The spoke routers are remotes sites, and they have two connections for redundancy, not so they can transit traffic between Router A and Router B. • Router A should never use the spokes as a path to anything reachable through Router B, so there’s no reason to learn about, or query for, routes through these spokes. A B 10.1.1.0/24 Router B Router A Spoke 4 Spoke 3 Spoke 2 Spoke 1

  14. Scalability – Limiting Queries:EIGRP Stub Routing • The EIGRP Stub Routing feature: • Improves network stability • Reduces resource utilization and • Simplifies remote router (spoke) configuration • Stub routing is commonly used in hub-and-spoke topology. • Stub router sends a special peer information packet to all neighboring routers to report its status as a stub router. • Any neighbor that receives a packet informing it of the stub status does not query the stub router for any routes.

  15. Scalability – Limiting QueriesEIGRP Stub Routing Hub Network Reply Query To inform Routers A & B B that the paths through the spokes should not be used for transit traffic, the spoke routers can be configured as stubs: A B 10.1.1.0/24 Router B Router A Spoke 4 Spoke 3 Spoke1(config)router eigrp 100 Spoke1(config-router)#eigrp stub Spoke 2 Spoke 1

  16. EIGRP- Issues with redundant network Can you identify problems with reudundancy in the network

  17. Solution- EIGRP- Issues with redundant network Several solutions to problem in the last slide: • Add a redundant Ethernet link between routers A and B to contain the backbone traffic to the hub site • Use some level of route summarization to limit the extents of the EIGRP QUERY mechanism. • Configure a distribute-list to limit the networks advertised by the spoke routers. • Best Solution: is to control traffic flows and limit query depth using EIGRP Stub Router functionality

  18. Configuring EIGRP Stub Eigrpstub configuration need only be entered on the spoke routers. Router(config-router)#eigrp stub [receive-only|connected|static|summary] • receive-only: Prevents the stub from sending any type of route. • connected: Permits stub to send connected routes (may still need to redistribute). • static: Permits stub to send static routes (must still redistribute). • summary:Permits stub to send summary routes. • Default is connected and summary.

  19. Automatic Summarisation Update: C- 2.0.0.0/8 C –2.0.0.0/8 Subnet 2.1.1.0/24 C – 2.0.0.0/8 Subnet 2.2.2.0/24 • EIGRP automatically summarises routes at the classful boundary—the boundary where the network address ends as defined by class-based addressing. • In most cases, auto summarisation is beneficial, because it keeps the routing tables as compact as possible. • Auto summarisation causes problems when two subnets are discontiguous.

  20. Null0 Summary Route • EIGRP automatically includes a null0 summary route as a child • route whenever bothof following conditions exist: • There is at least one subnet that was learned via EIGRP. • Automatic summarisation is enabled.

  21. Null0 Summary Route • EIGRP uses the Null0 interface to discard any packets that match the parent route but do not match any of the child routes. • Even with classless routing behavior configured, where the route lookup process will check for supernets and default routes, EIGRP will use the Null0 summary route and discard the packet because this route will match any packets of the parent that do not have a child route.

  22. R2 R3 R1 Performance - EIGRP Manual Summarisation 172.16.2.0/24 Loopback 10.1.1.1/30 ISP .1 S0/0/0 S0/0/1 DCE 172.16.3.0/24 192.168.10.8/30 .2 .9 192.168.1.0/24 S0/0/0 DCE S0/0/1 64 kbps 1024 kbps Fa0/0 Fa0/0 .10 .1 S0/0/1 172.16.1.0/24 .1 1544 kbps S0/0/0 DCE .1 .5 .6 Lo2 192.168.2.1/24 192.168.10.4/30 Lo2 192.168.3.1/24

  23. Bandwidth Optimisation- Configuring WAN Links • By default, EIGRP may use up to 50 % of the bandwidth of an interface or sub-interface for routing traffic. • EIGRP uses the bandwidth specified with the bandwidth command, or the default bandwidth of the link if none is configured, when calculating how much bandwidth to use. • EIGRP bandwidth usage can be adjusted as follows: R1(config)#interface s0/0/0 R1(config-if)#bandwidth 128 R1(config-if)#ip bandwidth-percentage eigrp 1 25 AS %

  24. Security :Simple Password vs. MD5 Authentication • Simple password authentication: • Router sends packet and key. • Neighbor checks if received key matches its key. • Not secure. • MD5 authentication • Configure a “key” (password) and key-id; router generates a message digest, or hash, of the key, key-id and message. • Message digest is sent with packet; key is not sent. • Secure.

  25. Security - EIGRP MD5 Authentication Configuration R1(config)#interface Serial0/0/1 R1(config-if)#bandwidth 64 R1(config-if)# ip address 192.168.1.101 255.255.255.224 R1(config-if)# ip authentication mode eigrp 100 md5 R1(config-if)# ip authentication key-chain eigrp 100 R1chain R1(config)# key chain R1chain R1(config-keychain)#key 1 R1(config-keychain-key)#key-string firstkey R1(config-keychain-key)# accept-lifetime 04:00:00 Jan 1 2006 infinite R1(config-keychain-key)# send-lifetime 04:00:00 Jan 1 2006 04:30:00 Jan 1 2006 R1(config-keychain)# key 2 R1(config-keychain-key)#key-string secondkey R1(config-keychain-key)#accept-lifetime 04:00:00 Jan 1 2006 infinite R1(config-keychain-key)#send-lifetime 04:29:00 Jan 1 2006 infinite

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