diff --git a/ex4.html b/ex4.html
index 2897609..cae0e42 100644
--- a/ex4.html
+++ b/ex4.html
@@ -176,7 +176,10 @@
         }},
         { selector: 'edge[label]', style: { 'label': 'data(label)' }},
         { selector: 'edge.route', style: { 'line-style': 'dashed','line-color': '#94a3b8','target-arrow-color': '#94a3b8' }},
-        { selector: 'edge.sg-attach', style: { 'line-style': 'dotted','line-color': '#f59e0b','target-arrow-color': '#f59e0b' }}
+        { selector: 'edge.sg-attach', style: { 'line-style': 'dotted','line-color': '#f59e0b','target-arrow-color': '#f59e0b' }},
+        { selector: 'edge.sg-sg', style: { 'line-color': '#f59e0b','target-arrow-color': '#f59e0b','source-arrow-color': '#f59e0b' }},
+        { selector: 'edge.sg-sg[tarrow > 0]', style: { 'target-arrow-shape': 'triangle' }},
+        { selector: 'edge.sg-sg[sarrow > 0]', style: { 'source-arrow-shape': 'triangle' }}
       ]
     });
 
@@ -219,6 +222,32 @@
         const label = `${sg.name || sg.id}\ningress: ${(rin[0]||'—')}${rin.length>1?'…':''}`;
         elements.push({ data: { id: sg.id, type: 'sg', label, rules: { in: rin, out: rout } } });
       }
+      // SG<->SG edges based on rules referencing other SGs
+      function parseSgRef(rule){
+        // match: "proto port from sg-xxxx"
+        const m = (rule||'').match(/^(\S+)\s+([^\s]+)\s+from\s+(sg-[0-9a-zA-Z]+)/);
+        if(!m) return null; return { proto:m[1], port:m[2], sg:m[3] };
+      }
+      const pairMap = new Map(); // key: A|B -> {inOn:{}, outFrom:{}}
+      function keyAB(a,b){ return a<b ? (a+'|'+b) : (b+'|'+a); }
+      function ensurePair(a,b){ const k=keyAB(a,b); if(!pairMap.has(k)) pairMap.set(k,{inOn:{},outFrom:{}}); return pairMap.get(k); }
+      function addIn(target, src, proto, port){ const p=ensurePair(target,src); (p.inOn[target]||(p.inOn[target]=[])).push({proto,port,src}); }
+      function addOut(src, target, proto, port){ const p=ensurePair(src,target); (p.outFrom[src]||(p.outFrom[src]=[])).push({proto,port,target}); }
+      for (const sg of sgs) {
+        for (const r of (sg.rules_in||[])) { const x=parseSgRef(r); if(x && sgById[x.sg]) addIn(sg.id, x.sg, x.proto, x.port); }
+        for (const r of (sg.rules_out||[])) { const x=parseSgRef(r); if(x && sgById[x.sg]) addOut(sg.id, x.sg, x.proto, x.port); }
+      }
+      function summarize(list){ const uniq=new Set(); for(const it of (list||[])){ const text=`${it.proto} ${it.port}`; uniq.add(text); } return Array.from(uniq).join(', '); }
+      for (const [k, val] of pairMap.entries()){
+        const [a,b]=k.split('|');
+        const s=a, t=b; // orient stable by id
+        const s2tList = (val.outFrom[s]||[]).concat(val.inOn[t]||[]);
+        const t2sList = (val.outFrom[t]||[]).concat(val.inOn[s]||[]);
+        const tarrow = s2tList.length ? 1 : 0; // arrow at target if flow S->T
+        const sarrow = t2sList.length ? 1 : 0; // arrow at source if flow T->S
+        const label = [summarize(s2tList), summarize(t2sList)].filter(Boolean).join(' | ');
+        elements.push({ data: { id:`sg:${s}|${t}`, source:s, target:t, label, tarrow, sarrow }, classes:'sg-sg' });
+      }
       // EC2
       for (const i of ec2s) {
         const label = `${i.name || i.id}\n${i.id}\n${i.type || ''}\n${i.privateIp ? ('Private IP: ' + i.privateIp) : ''}`;
@@ -431,7 +460,7 @@
 
       document.getElementById('toggle-sg').addEventListener('change',(e)=>{
         const show=e.target.checked;
-        cy.batch(()=>{ cy.nodes('[type = "sg"]').style('display', show?'element':'none'); cy.edges('.sg-attach').style('display', show?'element':'none'); });
+        cy.batch(()=>{ cy.nodes('[type = "sg"]').style('display', show?'element':'none'); cy.edges('.sg-attach, .sg-sg').style('display', show?'element':'none'); });
       });
       document.getElementById('toggle-routes').addEventListener('change',(e)=>{
         const show=e.target.checked;
@@ -470,6 +499,12 @@
         });
         cy.fit(undefined,24);
       }
+      async function tryLoadStartupLayout(){
+        try{
+          const resp = await fetch('layout.json', { cache: 'no-cache' });
+          if(resp && resp.ok){ const data = await resp.json(); applyLayoutData(data); }
+        }catch(e){ /* ignore if missing */ }
+      }
       document.getElementById('btn-save').addEventListener('click',()=> downloadJSON(snapshotLayout(),'vpc-layout.json'));
       document.getElementById('btn-load').addEventListener('click',()=> document.getElementById('load-file').click());
       document.getElementById('load-file').addEventListener('change',(e)=>{
@@ -494,6 +529,8 @@
       const LKEY='vpc-layout-autosave';
       function saveLocal(){ try{ localStorage.setItem(LKEY, JSON.stringify(snapshotLayout())); }catch{} }
       function restoreLocal(){ try{ const raw=localStorage.getItem(LKEY); if(raw) applyLayoutData(JSON.parse(raw)); }catch{} }
+      // Load file-based layout first (if present), then restore any local override
+      await tryLoadStartupLayout();
       restoreLocal();
       cy.on('position','node', saveLocal);
       cy.on('mouseup', ()=> { if(labelMode) saveLocal(); });