EIGRP Dmitry Figol CCIE R&S #53592 dmfigol.me August, 2016 Updated: July, 2017 

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Out of scope 3 • EIGRP PE-CE for MPLS L3VPN • EIGRP Over The Top (OTP) • EIGRP Stub Site (IWAN) • EIGRP Multi Topology Routing (MTR) in Named mode 

Quick facts 4 • Distance-vector routing protocol • Classless • Supports unequal cost load-balancing • Can provide sub-second convergence • Partial and bounded updates • Uses Diffusing Update Algorithm (DUAL) • Arbitrary route summarization 

Transport 5 • Uses multicast address 224.0.0.10 • Uses Reliable Transport Protocol (RTP) for transport – IP Protocol Number 88 • RTP can provide reliable delivery like TCP using sequence numbers • EIGRP uses both multicast and unicast packets 

Packets 6 • Hello • ACK – hello with no data • Update • Query • Reply • SIA query/reply • Goodbye – hello with K values set to 255 

Timers 7 • Hello timer (config-if)# ip hello-interval eigrp as seconds • Default is 5 seconds (on multipoint) or 60 seconds (on p2p) • Hold timer (config-if)# ip hold-interval eigrp as seconds • Default is 15 seconds (on multipoint) or 180 seconds (on p2p) • Active timer (config-router)# timers active-time minutes • Default is 3 minutes • SIA retransmit timer • Default is 90 seconds 

Adjacency 8 • To establish adjacency the following parameters should match: • AS number • K-values • Common subnet • Authentication type/password • Automatic neighbor discovery is configured using network command. (сonfig)# router eigrp as (config-router)# network • Enables EIGRP on all interfaces where IP addresses match subnet + wild card mask AND advertises the original prefix from the interface • Manual neighbor can be configured using: (config-router)# neighbor • Must be configured on both neighbors. The command also turns off sending and receiving multicast hello • Verification: # show ip eigrp neighbors [detail] 

9 • You can stop processing and sending any EIGRP packets on the interface using passive interface feature: (config-router)# passive-interface [default | int-name] • Manual neighbors will also stop working on this link, unlike in RIP Passive interface 

Administrative distance 10 • EIGRP uses the following administrative distances: • Internal – 90 • External – 170 • Summary – 5 • AD for internal and external routes can be changed globally using: (config-router)# distance eigrp int-ad ext-ad • AD for internal routes can be changed per prefix/neighbor using: (config-router)# distance ad neighbor-ip wc-mask acl • AD for external routes can’t be changed per prefix • AD for summary routes can be changed per prefix using: (config-router)# summary-metric prefix/length distance ad 

Composite metric 11 • EIGRP calculates composite metric using the formula: where • delaytotal – in microseconds, bandwidthmin – in kbps, load is the highest along the path, reliability is the lowest. • If K5 = 0, the formula changes: last multiplier is excluded • Note: load/reliability are not updated live, the current values are sent with a new update • Note: composite metric is never sent to the neighbor, only individual components 256 ∗ (1 ∗ ℎ + 2 ∗ ℎ 256 − + 3 ∗ ) ∗ 5 + 4 ℎ = 107 ℎ = 10 

EIGRP terms and definitions 12 • Computed Distance (CD) – composite metric of the whole path • Advertised Distance (AD) or Reported Distance (RD) – composite metric of the best path from neighbor’s perspective • Feasible Distance (FD) – the lowest value of CD of the best path since the last transition from Active to Passive • Note: FD does not always equal CD of the best path • Feasible Successor (FS) – the path that meets Feasibility Condition (FC), guaranteed to be loop-free by DUAL • Feasibility Condition (FC): RD of the candidate path < FD • Successor (S) – one of FS with the lowest CD 

Loop prevention 13 • Feasibility Condition • Split horizon – technically not needed as FC already guarantees loop- free path • Hop count (config-router)# metric maximum-hops 1..255 ! default is 100 • Router ID for external routes 

Operation 14 • EIGRP puts all received routes into Topology Table • Runs local computation and finds FS/S • The best path (or several) are then presented to RIB • Converged routes are marked as Passive • If there is reconvergence event, it is possible that route will go to Active state • Verification: # show ip eigrp topology [all-links] # show ip eigrp topology prefix/len 

15 Scenario 

Scenario – rules and task Rules: • If some EIGRP setting is not mentioned, assume default. • K3=1, K1=K2=K4=K5=0 • Delay is written above each link. Please note that you don’t need to divide microseconds by 10 and then multiply by 256, you can add metrics blindly just for the sake of this exercise • All questions are asked from perspective of R1 towards destination prefix 6.6.6.6/32 Task: • Which router is Successor? • What is the value of FD? • Fill in the table with ✓ or ✗ and write down the number of ticks # ✓ = ? 16 path via .. in topology table? is FS/S? (yes or no) R2 R3 R4 R5 

Scenario – answers 17 • Which router is Successor? R3 • What is the value of FD? 110 • Fill in the table with ✓ or ✗ and write down the number of ticks Pitfall: R4 will choose the path to the destination via R1 because 115 < 120. Because the best path is via R1, R4 will send an update with infinite metric to R1 due to split-horizon on R4 link to R1 path via .. in topology table? is FS/S? (yes or no) R2 ✓ ✗ R3 ✓ ✓ R4 ✗ ✗ R5 ✓ ✓ # ✓ = 5 

Unequal cost load balancing 18 • EIGRP supports unequal cost load balancing • The path is considered for load balancing if it is FS • Also the metric of the path must follow this inequality: CD of FS <= CD of S x Variance • Variance is configured using: (config-router)# variance number ! default is 1 • Number of maximum paths for load balancing is configured using: (config-router)# maximum-paths number ! default is 4, maximum is 32 

Reconvergence 19 • If we lose Successor, two scenarios are possible: • If there is no FS: • The route goes to Active state • Router sends QUERY to all neighbors • During QUERY process the route is frozen in RIB/topology table • Local computation of FS/S is done after we receive REPLY for all queries • If there is FS: • FS with the lowest CD becomes Successor* • The route stays passive • Results in sub-second convergence *Note: If we lose successor and the path with the lowest CD is not in FS list, the route goes to Active state regardless if we have other FS or not. 

Reconvergence – Query/Reply 20 • Query checks if neighbors have FS/S • Query also informs neighbors about the lost path (poisons with infinite metric) and they remove this path from the topology table • Conditions to send a REPLY to a received QUERY: • If we have a Successor, reply with the metric of the Successor • If the route is already in Active state, reply with infinite metric • If this route is NOT in the topology table, reply with infinite metric • Otherwise the route goes into ACTIVE state, queries are sent to all non- stub neighbors except of the neighbor from which QUERY was received. Upon receiving all replies, local computation is performed (FS/S is selected) and REPLY to the original QUERY is sent. • Stub router CAN send query to another stub router 

Reconvergence - Stuck in Active 21 • If all replies are not heard within Active timer (3 minutes) the route will go to SIA state and the neighbor from which we didn’t receive reply will be declared down • This behavior was changed with introduction of new packet types: SIA query/reply • After half of Active timer (SIA retransmit timer - 90 seconds), SIA query is sent to check the status of the query/neighbor and Active timer is reset • Neighbor must respond with Reply (if the route is not in topology table or if Successor has been found) or with SIA reply (if the route is still in Active) • If Reply or SIA reply is not heard, adjacency will be torn down • If Reply is not heard after three SIA query attempts, adjacency will be torn down 

Reconvergence (cont.) 22 • Reconvergence is the function of a query domain: more routers have to be queried, slower the process is. Also, more routers increase the chance of SIA. • To speed up convergence we should limit the query domain using: • Stub feature • Summarization • Filtering 

Path manipulation 23 • The metric can be influenced by changing individual metric components • Recommended to use delay to change the metric as it is the only cumulative parameter • Changing the bandwidth does not always change the metric • Changing the bandwidth can also influence other features like QoS 

Path manipulation – offset-list 24 • You can add specific value to the composite metric inbound or outbound per prefix using: (config-router)# offset-list [0 | acl] [in | out] [int-name] • Note: offset-list does “reverse engineering” in order to find a delay which will cause required change in composite metric. It means that offset-list affects only cumulative delay. If K3 = 0, offset-list will not work • Note: with offset-list you can increase metric to such a high value, that the route will not be installed in RIB (232) 

Filtering – distribute-list 25 • You can filter an update inbound or outbound using distribute-list: (config-router)# distribute-list [route-map map | prefix prefix-list [gateway prefix-list] | acl] [in | out] [int-name] • You can specify allowed list of routes and neighbors using gateway keyword with prefix-list. • You can also use extended ACL for ”per-neighbor” filtering: • Source field in ACL is responsible for the source of the route (neighbor’s IP address) • Destination field in ACL is responsible for the prefix itself (subnet mask is not matched) 

Filtering – tagging 26 • Using route-map in redistribution or in distribute-list you can tag internal and external routes and then filter them based on tag • Tags are 32-bit integer and can be represented in dotted-decimal format using: (config)# route-tag notation dotted-decimal • You can also match tag using wildcard: (config)# route-tag list tag-list permit ip wildcard (config)# route-map map permit 10 (config-route-map)# match tag list tag-list • Refer to the following article for more information EIGRP Route Tag Enhancements 

Summarization 27 • You can summarize networks on any router in EIGRP domain using: (config-if)# ip summary-address eigrp as prefix subnet-mask [leak-map route-map] • By default specifics are suppressed. You can unsuppress them using leak-map keyword. By doing so you can achieve traffic engineering • EIGRP looks for the lowest metric from specific routes and uses it as a metric for the summary • Discard route (via Null0 with AD 5) is automatically created locally to prevent routing loops • You can set maximum AD 255 using summary-metric command, which will remove discard route from RIB and as the result neither summary nor specific routes will be sent to the neighbor 

Stub router 28 • You can mark non-transit routers as stub, so queries are not sent to them. • Configured using: (config-router)# eigrp stub [connected | summary | redistributed | static | leak-map route- map | receive-only] • Default is connected + summary • An argument indicates which routes a stub router will send to its neighbors • Using leak-map keyword you can leak any route in topology table • Note: queries are sent to stub routers by another stub routers. 

Verification 29 # show ip eigrp interfaces # show ip eigrp neighbors [detail] # show ip eigrp topology [all-links] # show ip eigrp topology prefix/len # show ip eigrp events # show eigrp protocols # debug eigrp packet # debug eigrp fsm 

Authentication 30 • Classic mode supports only MD5 authentication, which is configured using: (config-if)# ip authentication mode eigrp md5 • You also need to specify key-chain for authentication: (config-if)# ip authentication key-chain eigrp • If needed, you can configure automatic key rotation using accept- lifetime and send-lifetime under key chain configuration 

Named mode 31 • The main benefit of named mode is that the entire EIGRP configuration is located in a single place • Activated by: (config)# router eigrp process-name 

Named mode – Address family 32 • To enter address family configuration: (config-router)# address-family AFI SAFI [vrf vrf-name] autonomous- system as-num • For example: (config-router)# address-family ipv4 unicast autonomous-system 100 • This is where any configuration specific to EIGRP process itself is applied, like network and neighbor commands 

33 Named mode – Address family commands 

Named mode – AF-interface 34 • To enter af-interface configuration: (config-router-af)# af-interface | default • This is where interface specific configuration is applied, like passive- interface or summary-address 

35 Named mode – AF-interface commands 

Named mode – AF topology 36 • This section is related to Multi Topology Routing (MTR), which gives an ability to create different logical topologies over the same physical topology. • MTR is not supported in 15.x M/T code train • If MTR is not used, relevant commands should be entered under topology base • To enter topology base configuration: (config-router-af)# topology base • This is where commands like redistribute, distribute-list, offset-list, variance are applied 

37 Named mode – AF topology commands 

38 • Wide metrics • HMAC-SHA authentication • Add-path • Disabling EIGRP on specific interface • Default interface settings (af-interface default) • Unique IPv6 behavior • Default tagging all internal and external routes • Over the Top (OTP) – not covered in this presentation • Stub site (IWAN) – not covered in this presentation Named mode – Exclusive features 

39 Named mode – Wide metrics source: CCIE R&S Official Certification Guide 

40 • After calculation the metric is scaled down by EIGRP_RIB_SCALE variable, which is 128 by default. This is done because RIB supports only 32-bit values for metric • EIGRP_RIB_SCALE variable can be changed using: (config-router-af)# metric rib-scale 1..255 Named mode – Wide metrics (cont.) 

41 • Wide metric introduces new K coefficient – K6, which controls two new metric components: jitter and energy. • Currently are unavailable for configuration • Type of the metric (wide/normal) is NOT sent, so neighbor does not actually know how metric components were calculated previously • Can lead to inconsistent path selection if both wide and normal metrics are used in the network because of different delay calculation Named mode – Wide metrics (cont.) 

42 • Named mode supports HMAC-SHA authentication which is stronger than MD5. Also it provides anti-replay protection • HMAC-SHA authentication can be enabled on the link using: (config-router-af-interface)# authentication mode hmac-sha-256 Note: the neighbor must use named mode as well to form an adjacency Named mode – HMAC-SHA authentication 

43 • Add-path feature allows to send several best equal-cost routes to neighbors • Note: Useful in DMVPN Phase 2 scenarios where Hub will reflect best routes from spoke without changing next-hop • Note: Unequal cost load balancing (variance) should be disabled • Activated using the following command: (config-router-af-interface)# add-paths Named mode – Add-path 

44 • EIGRP process on a specific interface can be disabled using: (config-router-af-interface)# shutdown • Note: this will stop advertising an associated prefix into EIGRP, unlike with passive-interface command Named mode – Disabling EIGRP on interface 

Named mode – Unique IPv6 behavior 45 • When IPv6 unicast address family is entered, EIGRP is automatically enabled on all interfaces with IPv6 address • It is the easiest way to get IPv6 connectivity in your network 

46 • You can automatically tag all routes (to filter them later) using: (config-router-af)# eigrp default-route-tag • Refer to slide “Filtering – tagging” Named mode – Default tagging 

47 • Old classic mode configuration can be converted to the new syntax using: (config-router)# eigrp upgrade-cli process-name Note: appeared only in 15.4(2)T Named mode – Conversion from classic 

48 • Verification commands have new syntax: show eigrp protocols show eigrp address-family [ipv4 | ipv6] as-num interfaces [detail] show eigrp address-family [ipv4 | ipv6] as-num neighbors [detail] show eigrp address-family [ipv4 | ipv6] as-num topology [all-links] show eigrp address-family [ipv4 | ipv6] as-num events Note: Old syntax is still supported Named mode – Verification commands 

49 • RFC 7868 – EIGRP • Routing TCP/IP Volume 1, 2nd Edition (Jeff Doyle) • CCIE Routing and Switching v5.0, Volume 1 (Narbik Kocharians, Peter Paluch) • EIGRP Frequently Asked Questions • Glimpse of EIGRP named mode • Advances in EIGRP • EIGRP Route Tag Enhancements Additional Resources 

Thank you