{"id":3412,"date":"2026-10-27T11:41:36","date_gmt":"2026-10-27T18:41:36","guid":{"rendered":"https:\/\/cyber.mag212.com\/learn\/eigrp-cheat-sheet\/"},"modified":"2026-10-27T11:41:36","modified_gmt":"2026-10-27T18:41:36","slug":"eigrp-cheat-sheet","status":"publish","type":"page","link":"https:\/\/cyber.mag212.com\/fr\/learn\/eigrp-cheat-sheet\/","title":{"rendered":"Aide-m\u00e9moire EIGRP"},"content":{"rendered":"<style>\n.m212eg{background:#07111c;color:#e9f3fb;font:16px\/1.65 Inter,Arial,sans-serif;border-radius:14px;overflow:hidden;border:1px solid #1f3b4d}\n.m212eg *{box-sizing:border-box}\n.m212eg a{color:#3cc8e8}\n.m212eg .eg-hero{background:linear-gradient(115deg,#102f42,#07111c 67%);border-bottom:3px solid #46db82;padding:40px 32px 32px}\n.m212eg .eg-hero .brand{font-size:27px;font-weight:900;letter-spacing:2px}\n.m212eg .eg-hero .brand span{color:#46db82}\n.m212eg .eg-hero .kicker{color:#3cc8e8;font-weight:700;letter-spacing:2px;margin-top:22px}\n.m212eg .eg-title{font-size:clamp(30px,5vw,52px);line-height:1.08;margin:12px 0;color:#fff;max-width:1000px;border:0;padding:0}\n.m212eg h2{font-size:27px;color:#fff;line-height:1.2;margin:6px 0 12px}\n.m212eg h3{margin:22px 0 8px}\n.m212eg h4{color:#46db82;margin:16px 0 6px}\n.m212eg p{margin:0 0 12px}\n.m212eg .eg-hero p{max-width:800px;color:#bfd4e4}\n.m212eg .eg-toc{margin:20px 0 0;padding:0 24px;display:flex;gap:10px;flex-wrap:wrap}\n.m212eg .eg-toc a{border:1px solid #285269;padding:5px 10px;text-decoration:none;border-radius:6px;color:#c3e5e7;font-size:13px}\n.m212eg .eg-toc a:hover{border-color:#46db82;color:#46db82}\n.m212eg .eg-main{padding:10px 22px 30px}\n.m212eg .guide{background:#0e2132;border:1px solid #26516a;border-radius:18px;margin:22px 0;padding:26px 32px;box-shadow:0 10px 35px #02080d55;scroll-margin-top:110px}\n.m212eg .num{color:#46db82;font:700 13px\/1.4 Arial;letter-spacing:2px}\n.m212eg table{border-collapse:collapse;width:100%;font-size:14px;margin:14px 0}\n.m212eg th{text-align:left;background:#17394c;color:#46db82}\n.m212eg td,.m212eg th{padding:10px 12px;border:0;border-bottom:1px solid #244758;color:#e9f3fb}\n.m212eg th{color:#46db82}\n.m212eg code{color:#9cebd3;background:#0a1a29;border-radius:4px;padding:1px 4px;overflow-wrap:anywhere;font-family:\"Courier New\",monospace}\n.m212eg pre{background:#050e17;border:1px solid #24465b;border-radius:10px;padding:20px;color:#bcecd9;white-space:pre-wrap;overflow:auto;font:13px\/1.55 'Courier New',monospace;margin:8px 0 14px}\n.m212eg .diagram{width:100%;height:auto;border-radius:14px;border:1px solid #29495d;display:block;margin:10px 0}\n.m212eg .statgrid{display:grid;grid-template-columns:repeat(4,minmax(0,1fr));gap:12px;margin:12px 0}\n.m212eg .statgrid>div,.m212eg .mathlab,.m212eg .steps p{padding:15px;background:#102e40;border:1px solid #285267;border-radius:10px}\n.m212eg .steps p{margin-bottom:10px}\n.m212eg .statgrid b{display:block;font-size:25px;color:#46db82}\n.m212eg .statgrid small{display:block;color:#b1c9d7;line-height:1.4}\n.m212eg .qa b{display:block;margin-top:15px;color:#3cc8e8}\n.m212eg .qa p{margin-top:3px}\n.m212eg ul{padding-left:22px;margin:0 0 12px}\n.m212eg .note{font-size:13px;color:#a5b6c2}\n.m212eg .eg-foot{padding:22px;text-align:center;background:#030a12;color:#90b2c1;font-size:14px}\n@media(max-width:620px){.m212eg .guide{padding:18px}.m212eg .statgrid{grid-template-columns:repeat(2,1fr)}.m212eg table{font-size:12px}.m212eg td,.m212eg th{padding:7px}.m212eg .eg-hero{padding:28px 20px}}\n<\/style>\n<div class=\"m212eg\" id=\"m212-eigrp\"><div class=\"eg-hero\"><div class=\"brand\">MAG212 <span>CYBER<\/span><\/div><div class=\"kicker\">NETWORK ENGINEERING \u00b7 CCNA \/ CCNP \/ ENTERPRISE<\/div><h2 class=\"eg-title\">EIGRP Ultimate Cheat Sheet<\/h2><p style=\"font-size:23px\">Configuration, Commands, Troubleshooting &amp; Security<\/p><p>An original, step-by-step reference from protocol fundamentals and DUAL route selection to realistic IOS XE labs, named mode, HMAC authentication and incident diagnosis.<\/p><p><b>Published by MAG212 CYBER<\/b> \u00b7 Technical field guide \u00b7 October 2026<\/p><\/div><div class=\"eg-toc\"><a href=\"#s01\">01 EIGRP at a glance<\/a><a href=\"#s02\">02 Packet types, tables &amp; neighbors<\/a><a href=\"#s03\">03 DUAL: FD, RD, successor and feasible successor<\/a><a href=\"#s04\">04 Legacy metric &amp; wide metrics<\/a><a href=\"#s05\">05 Three-router original lab topology<\/a><a href=\"#s06\">06 Classic Cisco IOS XE configuration<\/a><a href=\"#s07\">07 Modern named mode configuration<\/a><a href=\"#s08\">08 EIGRP authentication &amp; hardening<\/a><a href=\"#s09\">09 Summarization, stubs &amp; unequal-cost load sharing<\/a><a href=\"#s10\">10 Verification command reference<\/a><a href=\"#s11\">11 Troubleshooting decision tree<\/a><a href=\"#s12\">12 Real troubleshooting scenarios<\/a><a href=\"#s13\">13 Exam-style Q&amp;A with explanations<\/a><a href=\"#s14\">14 Deployment checklist &amp; references<\/a><\/div><div class=\"eg-main\"><section class=\"guide\" id=\"s01\"><div class=\"num\">SECTION 01<\/div><h2>EIGRP at a glance<\/h2><p>EIGRP is an advanced distance-vector interior gateway protocol that uses the <strong>Diffusing Update Algorithm (DUAL)<\/strong> to converge and maintain loop-free paths. It is documented in informational RFC 7868; it is not an IETF Standards Track protocol.<\/p><div class=\"statgrid\"><div><b>88<\/b><small>IP protocol number (not TCP\/UDP port)<\/small><\/div><div><b>224.0.0.10<\/b><small>IPv4 multicast destination<\/small><\/div><div><b>90 \/ 170<\/b><small>Default internal \/ external Cisco AD<\/small><\/div><div><b>DUAL<\/b><small>Loop-free route computation<\/small><\/div><\/div><p><strong>Typical hello\/hold timers:<\/strong> 5\/15 seconds on most fast links and 60\/180 seconds on some low-speed NBMA links; platform and interface settings matter.<\/p><\/section><section class=\"guide\" id=\"s02\"><div class=\"num\">SECTION 02<\/div><h2>Packet types, tables &amp; neighbors<\/h2><table><tr><th>Packet<\/th><th>Purpose<\/th><\/tr><tr><td>Hello<\/td><td>Neighbor discovery and maintenance<\/td><\/tr><tr><td>Update<\/td><td>Advertise topology information<\/td><\/tr><tr><td>Query<\/td><td>Ask neighbors about an unavailable route<\/td><\/tr><tr><td>Reply<\/td><td>Respond to route query<\/td><\/tr><tr><td>Acknowledgment<\/td><td>Reliable Transport Protocol acknowledgment (often an empty Hello)<\/td><\/tr><\/table><p><strong>Neighbor table:<\/strong> EIGRP peers and reachability. <strong>Topology table:<\/strong> learned paths and DUAL state. <strong>Routing table:<\/strong> selected paths installed for forwarding. EIGRP uses RTP for ordered and reliable exchanges as needed.<\/p><\/section><section class=\"guide\" id=\"s03\"><div class=\"num\">SECTION 03<\/div><h2>DUAL: FD, RD, successor and feasible successor<\/h2><p><strong>Reported Distance (RD)<\/strong> is the metric advertised by a neighbor. <strong>Total distance via that neighbor<\/strong> is the neighbor RD plus the local link metric (conceptually; composite metrics depend on bandwidth\/delay). <strong>Successor<\/strong> is the selected next hop. <strong>Feasible successor<\/strong> is a loop-free backup that meets the feasibility condition: <code data-no-translation=\"\">neighbor RD &lt; current feasible distance (FD)<\/code>.<\/p><div class=\"mathlab\"><h4>Worked feasibility example (illustrative metric units)<\/h4><table><tr><th>Via<\/th><th>Neighbor RD<\/th><th>Total metric<\/th><th>Result<\/th><\/tr><tr><td>R2<\/td><td>15,000<\/td><td>25,000<\/td><td>Successor<\/td><\/tr><tr><td>R3<\/td><td>20,000<\/td><td>31,000<\/td><td>Feasible successor: 20,000 &lt; 25,000<\/td><\/tr><tr><td>R4<\/td><td>27,000<\/td><td>30,000<\/td><td>Not feasible under this FD<\/td><\/tr><\/table><\/div><p><strong>Important nuance:<\/strong> RFC 7868 defines FD as the least-known metric since the last transition from active to passive; it is not necessarily identical to the currently displayed successor&#8217;s total metric. A non-feasible path may still be useful after DUAL performs a diffusing computation.<\/p><\/section><section class=\"guide\" id=\"s04\"><div class=\"num\">SECTION 04<\/div><h2>Legacy metric &amp; wide metrics<\/h2><p>Classic EIGRP uses bandwidth and cumulative delay by default, with <code data-no-translation=\"\">K1=1, K2=0, K3=1, K4=0, K5=0<\/code>. A simplified classic default expression is <code data-no-translation=\"\">256 \u00d7 (10\u2077 \/ minimum bandwidth in kbps + sum of delays in tens of microseconds)<\/code>. Named mode can use wide metrics, which support higher-speed links and different scale factors. Always inspect metric calculations on the actual software release.<\/p><p><strong>Warning:<\/strong> Do not modify K-values casually. Mismatches can prevent neighbor relationships or produce inconsistent route selection.<\/p><\/section><section class=\"guide\" id=\"s05\"><div class=\"num\">SECTION 05<\/div><h2>Three-router original lab topology<\/h2><p>R1 is the core; R2 advertises <code data-no-translation=\"\">192.0.2.0\/24<\/code>; R3 advertises <code data-no-translation=\"\">198.51.100.0\/24<\/code>. These are documentation networks, not public production addressing. R1\u2013R2 uses <code data-no-translation=\"\">10.10.12.0\/30<\/code>, R1\u2013R3 uses <code data-no-translation=\"\">10.10.13.0\/30<\/code>, and R2\u2013R3 uses <code data-no-translation=\"\">10.10.23.0\/30<\/code>.<\/p><img decoding=\"async\" class=\"diagram\" src=\"data:image\/svg+xml;base64,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\" alt=\"Three-router EIGRP AS 100 lab topology\"><h3 style=\"color:#46db82\">Detailed topology: interfaces and failover<\/h3><p>Each transit subnet and interface is labeled. The R2\u2013R3 link provides redundant connectivity; an immediate DUAL backup requires the feasibility condition to be met.<\/p><img decoding=\"async\" class=\"diagram\" src=\"data:image\/svg+xml;base64,<svg xmlns="http://www.w3.org/2000/svg" width="1500" height="920" viewBox="0 0 1500 920">
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<text x="58" y="74" font-size="37" font-family="Arial" font-weight="bold" fill="#46DB82">MAG212 CYBER</text><text x="58" y="116" font-size="24" font-family="Arial" fill="#f5fafc">EIGRP AS 100 — TRIANGLE LAB &amp; FAILOVER DESIGN</text>
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<rect x="865" y="359" width="300" height="76" rx="11" fill="#0b2231" stroke="#3CC8E8"/><text x="1015" y="387" fill="#fff" font-weight="bold">R1 ↔ R3 · 10.10.13.0/30</text><text x="1015" y="413" fill="#b2d7e6">Gi0/1 .1 ↔ Gi0/0 .2</text>
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<rect x="618" y="174" width="264" height="132" rx="19" fill="#11334a" stroke="#46DB82" stroke-width="4"/><circle cx="750" cy="205" r="15" fill="none" stroke="#46DB82" stroke-width="3"/><path d="M736 205h28m-14-14v28" stroke="#46DB82" stroke-width="3"/><text x="750" y="251" font-size="30" font-weight="bold" fill="#fff">R1 · CORE</text><text x="750" y="278" font-size="19" fill="#46DB82">RID 10.100.1.1</text>
<rect x="245" y="540" width="270" height="135" rx="19" fill="#11334a" stroke="#3CC8E8" stroke-width="4"/><text x="380" y="594" font-size="31" font-weight="bold" fill="#fff">R2 · DIST</text><text x="380" y="626" font-size="19" fill="#3CC8E8">AS 100 / 2 peers</text>
<rect x="985" y="540" width="270" height="135" rx="19" fill="#11334a" stroke="#3CC8E8" stroke-width="4"/><text x="1120" y="594" font-size="31" font-weight="bold" fill="#fff">R3 · DIST</text><text x="1120" y="626" font-size="19" fill="#3CC8E8">AS 100 / 2 peers</text>
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<path d="M380 675V733M1120 675V733" stroke="#46DB82" stroke-width="5"/><g font-family="Arial" text-anchor="middle"><rect x="177" y="733" width="406" height="83" rx="12" fill="#102a2d" stroke="#46DB82"/><text x="380" y="764" font-weight="bold" font-size="22" fill="#fff">LAN A · 192.0.2.0/24</text><text x="380" y="790" font-size="17" fill="#bceedd">R2 Gi0/2: 192.0.2.1</text><rect x="917" y="733" width="406" height="83" rx="12" fill="#102a2d" stroke="#46DB82"/><text x="1120" y="764" font-size="22" font-weight="bold" fill="#fff">LAN B · 198.51.100.0/24</text><text x="1120" y="790" font-size="17" fill="#bceedd">R3 Gi0/2: 198.51.100.1</text></g>
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<rect x="60" y="170" width="430" height="138" rx="12" fill="#0a1c29" stroke="#335a70"/><text x="85" y="204" fill="#46DB82" font-family="Arial" font-size="21" font-weight="bold">DUAL FAILOVER</text><text x="85" y="238" fill="#e1edf4" font-size="18" font-family="Arial">Primary path fails → switch to feasible</text><text x="85" y="264" fill="#e1edf4" font-size="18" font-family="Arial">successor if feasibility condition holds.</text><text x="85" y="292" fill="#f6ba74" font-size="17" font-family="Arial">Backup availability is metric-dependent.</text>
<rect x="1010" y="171" width="432" height="138" rx="12" fill="#0a1c29" stroke="#335a70"/><text x="1034" y="204" fill="#3CC8E8" font-family="Arial" font-size="21" font-weight="bold">EIGRP NEIGHBOR CHECK</text><text x="1034" y="239" fill="#d7eefa" font-size="19" font-family="monospace">show ip eigrp neighbors</text><text x="1034" y="270" fill="#d7eefa" font-size="19" font-family="monospace">show ip eigrp topology</text>
<text x="60" y="872" fill="#a8bec9" font-family="Arial" font-size="18">Green = advertised LAN / router ID     Cyan = routed transit     Amber dashed = redundant transit link</text>
<text x="1444" y="873" text-anchor="end" fill="#46DB82" font-family="Arial" font-size="18">ILLUSTRATIVE LAB · DOCUMENTATION IP RANGES</text>
</svg>\" alt=\"Professional three-router EIGRP topology showing all IPs and interfaces\"><p>IP allocation: R1 = <code data-no-translation=\"\">.1<\/code> on both links to R2\/R3; R2 = <code data-no-translation=\"\">10.10.12.2<\/code>, <code data-no-translation=\"\">10.10.23.1<\/code>; R3 = <code data-no-translation=\"\">10.10.13.2<\/code>, <code data-no-translation=\"\">10.10.23.2<\/code>. Modify interface numbering to match your hardware or lab simulator.<\/p><\/section><section class=\"guide\" id=\"s06\"><div class=\"num\">SECTION 06<\/div><h2>Classic Cisco IOS XE configuration<\/h2><p>These examples assume Gi0\/0 and Gi0\/1 are the routed uplinks and a Loopback0 or Gi0\/2 LAN interface is already addressed. Configure IP interfaces first, then EIGRP:<\/p><h4>R1 \u2014 core<\/h4><pre data-no-translation=\"\">interface GigabitEthernet0\/0\n description TO-R2\n ip address 10.10.12.1 255.255.255.252\n no shutdown\ninterface GigabitEthernet0\/1\n description TO-R3\n ip address 10.10.13.1 255.255.255.252\n no shutdown\ninterface Loopback0\n ip address 10.100.1.1 255.255.255.255\nrouter eigrp 100\n eigrp router-id 10.100.1.1\n network 10.10.12.0 0.0.0.3\n network 10.10.13.0 0.0.0.3\n network 10.100.1.1 0.0.0.0\n passive-interface Loopback0<\/pre><h4>R2 \u2014 distribution<\/h4><pre data-no-translation=\"\">interface GigabitEthernet0\/0\n ip address 10.10.12.2 255.255.255.252\n no shutdown\ninterface GigabitEthernet0\/1\n ip address 10.10.23.1 255.255.255.252\n no shutdown\ninterface GigabitEthernet0\/2\n ip address 192.0.2.1 255.255.255.0\n no shutdown\nrouter eigrp 100\n network 10.10.12.0 0.0.0.3\n network 10.10.23.0 0.0.0.3\n network 192.0.2.0 0.0.0.255\n passive-interface GigabitEthernet0\/2<\/pre><h4>R3 \u2014 distribution<\/h4><pre data-no-translation=\"\">interface GigabitEthernet0\/0\n ip address 10.10.13.2 255.255.255.252\n no shutdown\ninterface GigabitEthernet0\/1\n ip address 10.10.23.2 255.255.255.252\n no shutdown\ninterface GigabitEthernet0\/2\n ip address 198.51.100.1 255.255.255.0\n no shutdown\nrouter eigrp 100\n network 10.10.13.0 0.0.0.3\n network 10.10.23.0 0.0.0.3\n network 198.51.100.0 0.0.0.255\n passive-interface GigabitEthernet0\/2<\/pre><p>Expected neighbor count: R1 sees R2 and R3; R2 sees R1 and R3; R3 sees R1 and R2. Verify with <code data-no-translation=\"\">show ip eigrp neighbors<\/code>.<\/p><\/section><section class=\"guide\" id=\"s07\"><div class=\"num\">SECTION 07<\/div><h2>Modern named mode configuration<\/h2><p>Named mode uses an EIGRP process name and IPv4 address family. The example below is for R1; adjust networks and router IDs on R2\/R3. Some platforms require explicit <code data-no-translation=\"\">no shutdown<\/code> on the address family.<\/p><pre data-no-translation=\"\">router eigrp MAG212\n address-family ipv4 unicast autonomous-system 100\n  eigrp router-id 10.100.1.1\n  network 10.10.12.0 0.0.0.3\n  network 10.10.13.0 0.0.0.3\n  network 10.100.1.1 0.0.0.0\n  af-interface Loopback0\n   passive-interface\n  exit-af-interface\n  no shutdown\n exit-address-family<\/pre><p>Do not run classic and named EIGRP configurations for the same routes without an intentional migration design. Use one method per lab.<\/p><\/section><section class=\"guide\" id=\"s08\"><div class=\"num\">SECTION 08<\/div><h2>EIGRP authentication &amp; hardening<\/h2><p><strong>Prefer authenticated adjacencies<\/strong> on supported platforms. Example, in named EIGRP mode on the R1\u2013R2 link (configure the same shared secret on both routers):<\/p><pre data-no-translation=\"\">router eigrp MAG212\n address-family ipv4 unicast autonomous-system 100\n  af-interface GigabitEthernet0\/0\n   authentication mode hmac-sha-256 0 LAB-REPLACE-WITH-STRONG-SECRET\n  exit-af-interface\n exit-address-family<\/pre><p>This is an educational example. Do not put real secrets in public configuration repositories; confirm platform support and secret-handling capabilities. Classic mode supports key chains with MD5, but MD5 is legacy. Security baseline: <strong>passive access-facing interfaces, filter redistributed routes, limit EIGRP to authorized links, use infrastructure ACLs, monitor neighbor changes and minimize routing privileges.<\/strong><\/p><\/section><section class=\"guide\" id=\"s09\"><div class=\"num\">SECTION 09<\/div><h2>Summarization, stubs &amp; unequal-cost load sharing<\/h2><p><strong>EIGRP stub<\/strong> reduces unnecessary queries toward a spoke or branch. <strong>Summarization<\/strong> can reduce table size and query scope, but only summarize networks that truly exist. <strong>Variance<\/strong> permits unequal-cost load balancing among eligible loop-free feasible paths, subject to configuration and platform limits.<\/p><pre data-no-translation=\"\">! Classic mode: branch router (example)\nrouter eigrp 100\n eigrp stub connected summary\n! Different design: optionally tune variance after analyzing path metrics\nrouter eigrp 100\n variance 2<\/pre><p><strong>Split horizon:<\/strong> leave it enabled unless a reviewed topology (such as some hub-and-spoke overlays) specifically requires an exception.<\/p><\/section><section class=\"guide\" id=\"s10\"><div class=\"num\">SECTION 10<\/div><h2>Verification command reference<\/h2><table><tr><th>Commande<\/th><th>Question it answers<\/th><\/tr><tr><td><code data-no-translation=\"\">show ip eigrp neighbors<\/code><\/td><td>Are peers established and stable?<\/td><\/tr><tr><td><code data-no-translation=\"\">show ip eigrp topology<\/code><\/td><td>What successor\/feasible paths exist?<\/td><\/tr><tr><td><code data-no-translation=\"\">show ip eigrp topology all-links<\/code><\/td><td>What alternative paths were learned?<\/td><\/tr><tr><td><code data-no-translation=\"\">show ip route eigrp<\/code><\/td><td>Which EIGRP routes made the RIB?<\/td><\/tr><tr><td><code data-no-translation=\"\">show ip protocols<\/code><\/td><td>Process, AS, networks, passive interfaces, timers?<\/td><\/tr><tr><td><code data-no-translation=\"\">show ip eigrp interfaces detail<\/code><\/td><td>Interface EIGRP details?<\/td><\/tr><tr><td><code data-no-translation=\"\">show ip eigrp traffic<\/code><\/td><td>Are queries\/replies\/updates increasing?<\/td><\/tr><tr><td><code data-no-translation=\"\">show logging | include DUAL|EIGRP<\/code><\/td><td>Recent adjacency and DUAL events?<\/td><\/tr><tr><td><code data-no-translation=\"\">show running-config | section router eigrp<\/code><\/td><td>What EIGRP configuration is active?<\/td><\/tr><\/table><p>Verify command syntax on your exact IOS XE version. Avoid production debugging without a maintenance plan.<\/p><\/section><section class=\"guide\" id=\"s11\"><div class=\"num\">SECTION 11<\/div><h2>Troubleshooting decision tree<\/h2><div class=\"steps\"><p><b>1 \u00b7 No neighbor?<\/b> Check link state, ping, IP\/mask, EIGRP AS, EIGRP-enabled interfaces, passive-interface status, authentication, K-values, and filtering of IP protocol 88.<\/p><p><b>2 \u00b7 Neighbor up, route missing?<\/b> Check network statements, topology table, distribute lists, summarization, route redistribution, and AD of competing protocols.<\/p><p><b>3 \u00b7 Route Active \/ SIA?<\/b> Check query propagation, unstable or slow links, CPU pressure, missing replies, and query scope; consider stub and summarization design.<\/p><p><b>4 \u00b7 Unexpected path?<\/b> Examine minimum bandwidth, cumulative delay, feasible condition, successors, variance, and administrative distance.<\/p><p><b>5 \u00b7 Flapping neighbor?<\/b> Investigate packet loss, interface errors, MTU-related exchange behavior, timer\/hold expiration, authentication mismatches and device resource load.<\/p><\/div><\/section><section class=\"guide\" id=\"s12\"><div class=\"num\">SECTION 12<\/div><h2>Real troubleshooting scenarios<\/h2><h4>Scenario A \u2014 EIGRP neighbors never appear<\/h4><p>R1 has <code data-no-translation=\"\">router eigrp 100<\/code>; R2 has <code data-no-translation=\"\">router eigrp 200<\/code>. <strong>Diagnosis:<\/strong> mismatched AS numbers. <strong>R\u00e9parer:<\/strong> place intended peers in the same EIGRP AS, confirm addresses\/network statements, then verify adjacency.<\/p><h4>Scenario B \u2014 LAN network not advertised<\/h4><p>R2 has the LAN configured but EIGRP enables only WAN network statements. <strong>Diagnosis:<\/strong> LAN interface not matched by EIGRP. <strong>R\u00e9parer:<\/strong> add <code data-no-translation=\"\">network 192.0.2.0 0.0.0.255<\/code> and make Gi0\/2 passive; passive means advertise connected subnet without sending hellos.<\/p><h4>Scenario C \u2014 backup route not shown as feasible successor<\/h4><p>The alternative RD is greater than or equal to the stored FD. <strong>Diagnosis:<\/strong> failed feasibility condition, not necessarily a broken path. <strong>R\u00e9parer:<\/strong> validate actual metrics and allow DUAL to recompute during failures; do not force metric changes solely to fill a backup slot.<\/p><\/section><section class=\"guide\" id=\"s13\"><div class=\"num\">SECTION 13<\/div><h2>Exam-style Q&amp;A with explanations<\/h2><div class=\"qa\"><b>Q1. Does EIGRP use TCP port 88?<\/b><p>No. It uses <strong>IP protocol number 88<\/strong>, not a TCP or UDP port.<\/p><b>Q2. Which route wins: internal EIGRP AD 90 or OSPF AD 110?<\/b><p>For identical prefix lengths and default administrative distances, internal EIGRP generally wins. Different prefixes use longest-prefix match first.<\/p><b>Q3. Is a neighbor&#8217;s RD of 30,000 feasible if stored FD is 25,000?<\/b><p>No. The feasibility condition is strictly <code data-no-translation=\"\">RD &lt; FD<\/code>.<\/p><b>Q4. Does passive-interface prevent advertisement?<\/b><p>No. It prevents neighbor formation\/hellos on that interface while its matched connected network can still be advertised.<\/p><b>Q5. Which EIGRP route code appears in the routing table?<\/b><p><code data-no-translation=\"\">D<\/code> identifies internal EIGRP and <code data-no-translation=\"\">D EX<\/code> external EIGRP in common IOS\/IOS XE outputs.<\/p><b>Q6. Why can a route go Active?<\/b><p>The router has lost a usable successor and has no immediately usable feasible successor, so DUAL requests information from neighbors.<\/p><b>Q7. What should you do before changing K-values?<\/b><p>Check platform behavior and ensure all intended peers have consistent metric settings; avoid changing K-values as a shortcut for traffic engineering.<\/p><b>Q8. Is EIGRP an IETF Standards Track protocol?<\/b><p>No. RFC 7868 is informational.<\/p><\/div><\/section><section class=\"guide\" id=\"s14\"><div class=\"num\">SECTION 14<\/div><h2>Deployment checklist &amp; references<\/h2><ul><li>Plan unique addresses and documentation-grade lab IPs.<\/li><li>Enable EIGRP only on intended networks and keep LAN ports passive.<\/li><li>Confirm adjacencies, topology and installed routes before traffic tests.<\/li><li>Require approved authentication on participating links where supported.<\/li><li>Limit route redistribution and summarize only where safe.<\/li><li>Collect baseline neighbor counts, CPU, route table and events.<\/li><li>Test controlled failover and restoration during a lab\/maintenance window.<\/li><\/ul><p><strong>Primary references:<\/strong> <a href=\"https:\/\/www.rfc-editor.org\/info\/rfc7868\/\" target=\"_blank\" rel=\"noopener\">RFC 7868<\/a> \u00b7 <a href=\"https:\/\/www.cisco.com\/c\/en\/us\/support\/docs\/ip\/enhanced-interior-gateway-routing-protocol-eigrp\/200156-Configure-EIGRP-Named-Mode.html\" target=\"_blank\" rel=\"noopener\">Cisco Named Mode Guide<\/a> \u00b7 <a href=\"https:\/\/www.cisco.com\/c\/en\/us\/td\/docs\/routers\/ios-xe\/ip-routing\/b-ip-routing\/m_ire-enhanced-igrp.html\" target=\"_blank\" rel=\"noopener\">Cisco IOS XE EIGRP Configuration<\/a> \u00b7 <a href=\"https:\/\/www.cisco.com\/c\/en\/us\/td\/docs\/ios-xml\/ios\/iproute_eigrp\/command\/ire-cr-book\/ire-a1.html\" target=\"_blank\" rel=\"noopener\">Cisco EIGRP Authentication Command Reference<\/a>.<\/p><p class=\"note\">This is independent original educational material for MAG212 CYBER. Command availability and syntax vary by software version and platform. Lab metrics and Q&#038;A scenarios are illustrative, not observed production telemetry.<\/p><\/section><\/div><div class=\"eg-foot\">MAG212 CYBER \u00b7 INSIGHTS TODAY. A SAFER TOMORROW. \u00b7 Educational use<br><a href=\"\/fr\/learn\/\">Plus de guides dans Apprendre<\/a> \u00b7 <a href=\"\/fr\/learn\/bgp-cheat-sheet\/\">Aide-m\u00e9moire BGP<\/a> \u00b7 <a href=\"\/fr\/services\/\">Conseil en r\u00e9seau et s\u00e9minaires<\/a><\/div><\/div>","protected":false},"excerpt":{"rendered":"<p>EIGRP field guide: DUAL, metrics, classic and named-mode IOS XE configs, HMAC-SHA-256 authentication and troubleshooting.<\/p>","protected":false},"author":1,"featured_media":0,"parent":3385,"menu_order":0,"comment_status":"closed","ping_status":"closed","template":"","meta":{"footnotes":""},"class_list":["post-3412","page","type-page","status-publish","hentry"],"_hostinger_reach_plugin_has_subscription_block":false,"_hostinger_reach_plugin_is_elementor":false,"_links":{"self":[{"href":"https:\/\/cyber.mag212.com\/fr\/wp-json\/wp\/v2\/pages\/3412","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/cyber.mag212.com\/fr\/wp-json\/wp\/v2\/pages"}],"about":[{"href":"https:\/\/cyber.mag212.com\/fr\/wp-json\/wp\/v2\/types\/page"}],"author":[{"embeddable":true,"href":"https:\/\/cyber.mag212.com\/fr\/wp-json\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"https:\/\/cyber.mag212.com\/fr\/wp-json\/wp\/v2\/comments?post=3412"}],"version-history":[{"count":0,"href":"https:\/\/cyber.mag212.com\/fr\/wp-json\/wp\/v2\/pages\/3412\/revisions"}],"up":[{"embeddable":true,"href":"https:\/\/cyber.mag212.com\/fr\/wp-json\/wp\/v2\/pages\/3385"}],"wp:attachment":[{"href":"https:\/\/cyber.mag212.com\/fr\/wp-json\/wp\/v2\/media?parent=3412"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}