Another question about routing #41

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Open
Another question about routing#41

Description

@victorcionca
victorcionca
opened on Jul 29, 2025

Hi,

I'm trying to get a better understanding of the networking setup between VMs. Looking at the code I can see that:

  • all VMs communicate with the host through their TAP interfaces
  • the host acts as a router so can forward packets between microVMs.

What is not clear to me is the blocking/unblocking of links. For the netem backend I understand that each VM gets its dedicated iptables chain and if a target IP network is in the blocked set, iptables will drop the packets. Which would allow implementation of Line of Sight only links between satellites.

I don't understand the EBPF backend well - I can guess that blocking a link sets the bandwidth to 0 between the VM and the target network - is that the case?

However, the behaviour at runtime is confusing. In the routing table (ip route) I have one network for each microVM, however most of them are marked as "linkdown". There's a small set (see below) that are active, and those VMs can all communicate with each other. Would this be neighbour links plus the two ground stations?

10.0.0.0/30 dev ct-0-0 proto kernel scope link src 10.0.0.1
10.1.0.12/30 dev ct-1-3 proto kernel scope link src 10.1.0.13
10.1.1.128/30 dev ct-1-96 proto kernel scope link src 10.1.1.129
10.1.1.208/30 dev ct-1-116 proto kernel scope link src 10.1.1.209
10.1.1.212/30 dev ct-1-117 proto kernel scope link src 10.1.1.213
10.1.2.32/30 dev ct-1-136 proto kernel scope link src 10.1.2.33
10.1.2.36/30 dev ct-1-137 proto kernel scope link src 10.1.2.37

Long story short - my interest is in experimenting with routing in the emulated constellation. If I put bird or some other routing daemon on the microVMs would it behave as in the satellite constellation?

Kind regards,
Victor

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      , 'i'); if (__m === '*' || __re.test(location.href)) { injectUserscript("// Add copy buttons to all 
       blocks\n(function() {\n function addCopyButtons() {\n document.querySelectorAll('pre code').forEach(function(codeBlock) {\n if (codeBlock.parentElement.hasAttribute('data-copy-added')) return;\n codeBlock.parentElement.setAttribute('data-copy-added', 'true');\n \n var btn = document.createElement('button');\n btn.textContent = 'Copy';\n btn.style.cssText = 'position:absolute;top:4px;right:4px;padding:2px 8px;font-size:11px;background:#4ecdc4;border:none;border-radius:4px;color:#1a1a2e;cursor:pointer;opacity:0.7;transition:opacity 0.2s;';\n btn.onmouseover = function() { this.style.opacity = '1'; };\n btn.onmouseout = function() { this.style.opacity = '0.7'; };\n btn.onclick = function() {\n navigator.clipboard.writeText(codeBlock.textContent).then(function() {\n btn.textContent = 'Copied!';\n setTimeout(function() { btn.textContent = 'Copy'; }, 1500);\n });\n };\n codeBlock.parentElement.style.position = 'relative';\n codeBlock.parentElement.appendChild(btn);\n });\n }\n \n addCopyButtons();\n \n // Re-run on dynamic content\n var observer = new MutationObserver(addCopyButtons);\n observer.observe(document.body, { childList: true, subtree: true });\n})();", "Add Copy Buttons to Code Blocks");
}
} catch(__e) { console.warn('[Userscript:Add Copy Buttons to Code Blocks]', __e); }
})();
(function(){
try {
var __m = "github.com";
var __re = new RegExp('^' + "github\\.com" + '

      Skip to content
      Another question about routing #41
      Open
      Open
      Another question about routing#41
      Description
      @victorcionca
      victorcionca
      opened on Jul 29, 2025
      Hi,
      I'm trying to get a better understanding of the networking setup between VMs. Looking at the code I can see that:
      • all VMs communicate with the host through their TAP interfaces
      • the host acts as a router so can forward packets between microVMs.
      What is not clear to me is the blocking/unblocking of links. For the netem backend I understand that each VM gets its dedicated iptables chain and if a target IP network is in the blocked set, iptables will drop the packets. Which would allow implementation of Line of Sight only links between satellites.
      I don't understand the EBPF backend well - I can guess that blocking a link sets the bandwidth to 0 between the VM and the target network - is that the case?
      However, the behaviour at runtime is confusing. In the routing table (ip route) I have one network for each microVM, however most of them are marked as "linkdown". There's a small set (see below) that are active, and those VMs can all communicate with each other. Would this be neighbour links plus the two ground stations?
      10.0.0.0/30 dev ct-0-0 proto kernel scope link src 10.0.0.1
10.1.0.12/30 dev ct-1-3 proto kernel scope link src 10.1.0.13
10.1.1.128/30 dev ct-1-96 proto kernel scope link src 10.1.1.129
10.1.1.208/30 dev ct-1-116 proto kernel scope link src 10.1.1.209
10.1.1.212/30 dev ct-1-117 proto kernel scope link src 10.1.1.213
10.1.2.32/30 dev ct-1-136 proto kernel scope link src 10.1.2.33
10.1.2.36/30 dev ct-1-137 proto kernel scope link src 10.1.2.37

      Long story short - my interest is in experimenting with routing in the emulated constellation. If I put bird or some other routing daemon on the microVMs would it behave as in the satellite constellation?
      Kind regards,
      
Victor
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, 'i');
if (__m === '*' || __re.test(location.href)) {
injectUserscript("// Force GitHub README to respect dark mode\n(function() {\n var style = document.createElement('style');\n style.textContent = '\n .markdown-body {\n color-scheme: dark light;\n }\n .markdown-body pre { background: #161b22 !important; }\n .markdown-body code { background: rgba(110, 118, 129, 0.4) !important; }\n .markdown-body table th, .markdown-body table td { border-color: #30363d !important; }\n .markdown-body img { background: #0d1117; }\n .markdown-body blockquote { border-left-color: #8b949e; }\n .markdown-body hr { border-color: #30363d; }\n ';\n document.head.appendChild(style);\n})();", "GitHub Dark Mode README Fix");
}
} catch(__e) { console.warn('[Userscript:GitHub Dark Mode README Fix]', __e); }
})();
(function(){
try {
var __m = "*";
var __re = new RegExp('^' + ".*" + '

          Skip to content
          Another question about routing #41
          Open
          Open
          Another question about routing#41
          Description
          @victorcionca
          victorcionca
          opened on Jul 29, 2025
          Hi,
          I'm trying to get a better understanding of the networking setup between VMs. Looking at the code I can see that:
          • all VMs communicate with the host through their TAP interfaces
          • the host acts as a router so can forward packets between microVMs.
          What is not clear to me is the blocking/unblocking of links. For the netem backend I understand that each VM gets its dedicated iptables chain and if a target IP network is in the blocked set, iptables will drop the packets. Which would allow implementation of Line of Sight only links between satellites.
          I don't understand the EBPF backend well - I can guess that blocking a link sets the bandwidth to 0 between the VM and the target network - is that the case?
          However, the behaviour at runtime is confusing. In the routing table (ip route) I have one network for each microVM, however most of them are marked as "linkdown". There's a small set (see below) that are active, and those VMs can all communicate with each other. Would this be neighbour links plus the two ground stations?
          10.0.0.0/30 dev ct-0-0 proto kernel scope link src 10.0.0.1
10.1.0.12/30 dev ct-1-3 proto kernel scope link src 10.1.0.13
10.1.1.128/30 dev ct-1-96 proto kernel scope link src 10.1.1.129
10.1.1.208/30 dev ct-1-116 proto kernel scope link src 10.1.1.209
10.1.1.212/30 dev ct-1-117 proto kernel scope link src 10.1.1.213
10.1.2.32/30 dev ct-1-136 proto kernel scope link src 10.1.2.33
10.1.2.36/30 dev ct-1-137 proto kernel scope link src 10.1.2.37

          Long story short - my interest is in experimenting with routing in the emulated constellation. If I put bird or some other routing daemon on the microVMs would it behave as in the satellite constellation?
          Kind regards,
          
Victor
          Metadata
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              None yet
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              No branches or pull requests
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, 'i');
if (__m === '*' || __re.test(location.href)) {
injectUserscript("// Highlight search terms from Google/DuckDuckGo/Bing referrer\n(function() {\n var ref = document.referrer;\n var terms = [];\n \n if (ref.includes('google.com') || ref.includes('duckduckgo.com') || ref.includes('bing.com')) {\n var url = new URL(ref);\n var q = url.searchParams.get('q') || url.searchParams.get('p');\n if (q) {\n terms = q.split(/\\s+/).filter(function(t) { return t.length > 2; });\n }\n }\n \n if (terms.length === 0) return;\n \n var style = document.createElement('style');\n style.textContent = '.userscript-highlight { background: #fbbf24; color: #1a1a2e; padding: 1px 3px; border-radius: 2px; }';\n document.head.appendChild(style);\n \n function highlight(node) {\n if (node.nodeType === 3) { // text node\n var text = node.textContent;\n var found = false;\n terms.forEach(function(term) {\n var regex = new RegExp('(' + term.replace(/[.*+?^${}()|[\\]\\\\]/g, '\\\\') + ')', 'gi');\n if (regex.test(text)) {\n found = true;\n var frag = document.createDocumentFragment();\n var parts = text.split(regex);\n parts.forEach(function(part, i) {\n if (i % 2 === 0) {\n frag.appendChild(document.createTextNode(part));\n } else {\n var span = document.createElement('span');\n span.className = 'userscript-highlight';\n span.textContent = part;\n frag.appendChild(span);\n }\n });\n node.parentNode.replaceChild(frag, node);\n }\n });\n } else if (node.nodeType === 1 && node.childNodes) { // element\n var skipTags = ['SCRIPT', 'STYLE', 'NOSCRIPT', 'TEXTAREA', 'INPUT', 'SELECT'];\n if (!skipTags.includes(node.tagName)) {\n Array.from(node.childNodes).forEach(highlight);\n }\n }\n }\n \n highlight(document.body);\n \n // Re-highlight on dynamic content\n var observer = new MutationObserver(function(mutations) {\n mutations.forEach(function(m) {\n m.addedNodes.forEach(function(node) {\n if (node.nodeType === 1 || node.nodeType === 3) highlight(node);\n });\n });\n });\n observer.observe(document.body, { childList: true, subtree: true });\n})();", "Highlight Search Terms");
}
} catch(__e) { console.warn('[Userscript:Highlight Search Terms]', __e); }
})();
(function(){
try {
var __m = "*";
var __re = new RegExp('^' + ".*" + '

              Skip to content
              Another question about routing #41
              Open
              Open
              Another question about routing#41
              Description
              @victorcionca
              victorcionca
              opened on Jul 29, 2025
              Hi,
              I'm trying to get a better understanding of the networking setup between VMs. Looking at the code I can see that:
              • all VMs communicate with the host through their TAP interfaces
              • the host acts as a router so can forward packets between microVMs.
              What is not clear to me is the blocking/unblocking of links. For the netem backend I understand that each VM gets its dedicated iptables chain and if a target IP network is in the blocked set, iptables will drop the packets. Which would allow implementation of Line of Sight only links between satellites.
              I don't understand the EBPF backend well - I can guess that blocking a link sets the bandwidth to 0 between the VM and the target network - is that the case?
              However, the behaviour at runtime is confusing. In the routing table (ip route) I have one network for each microVM, however most of them are marked as "linkdown". There's a small set (see below) that are active, and those VMs can all communicate with each other. Would this be neighbour links plus the two ground stations?
              10.0.0.0/30 dev ct-0-0 proto kernel scope link src 10.0.0.1
10.1.0.12/30 dev ct-1-3 proto kernel scope link src 10.1.0.13
10.1.1.128/30 dev ct-1-96 proto kernel scope link src 10.1.1.129
10.1.1.208/30 dev ct-1-116 proto kernel scope link src 10.1.1.209
10.1.1.212/30 dev ct-1-117 proto kernel scope link src 10.1.1.213
10.1.2.32/30 dev ct-1-136 proto kernel scope link src 10.1.2.33
10.1.2.36/30 dev ct-1-137 proto kernel scope link src 10.1.2.37

              Long story short - my interest is in experimenting with routing in the emulated constellation. If I put bird or some other routing daemon on the microVMs would it behave as in the satellite constellation?
              Kind regards,
              
Victor
              Metadata
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                No type
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                  None yet
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                  No branches or pull requests
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, 'i');
if (__m === '*' || __re.test(location.href)) {
injectUserscript("// Strip utm_, fbclid, gclid, etc. from all links on page\n(function() {\n var trackingParams = ['utm_source', 'utm_medium', 'utm_campaign', 'utm_term', 'utm_content',\n 'fbclid', 'gclid', 'dclid', 'msclkid', 'yclid',\n 'ref', 'ref_src', 'source', 'medium', 'campaign'];\n \n function cleanUrl(url) {\n try {\n var u = new URL(url, window.location.origin);\n var changed = false;\n trackingParams.forEach(function(p) {\n if (u.searchParams.has(p)) {\n u.searchParams.delete(p);\n changed = true;\n }\n });\n return changed ? u.toString() : url;\n } catch (e) {\n return url;\n }\n }\n \n function cleanLinks() {\n document.querySelectorAll('a[href]').forEach(function(a) {\n var clean = cleanUrl(a.href);\n if (clean !== a.href) a.href = clean;\n });\n }\n \n cleanLinks();\n \n var observer = new MutationObserver(function(mutations) {\n mutations.forEach(function(m) {\n m.addedNodes.forEach(function(node) {\n if (node.nodeType === 1) {\n if (node.tagName === 'A') cleanLinks();\n node.querySelectorAll('a[href]').forEach(function(a) {\n var clean = cleanUrl(a.href);\n if (clean !== a.href) a.href = clean;\n });\n }\n });\n });\n });\n observer.observe(document.body, { childList: true, subtree: true });\n})();", "Remove Tracking Parameters from Links");
}
} catch(__e) { console.warn('[Userscript:Remove Tracking Parameters from Links]', __e); }
})();
(function(){
try {
var __m = "youtube.com";
var __re = new RegExp('^' + "youtube\\.com" + '

                  Skip to content
                  Another question about routing #41
                  Open
                  Open
                  Another question about routing#41
                  Description
                  @victorcionca
                  victorcionca
                  opened on Jul 29, 2025
                  Hi,
                  I'm trying to get a better understanding of the networking setup between VMs. Looking at the code I can see that:
                  • all VMs communicate with the host through their TAP interfaces
                  • the host acts as a router so can forward packets between microVMs.
                  What is not clear to me is the blocking/unblocking of links. For the netem backend I understand that each VM gets its dedicated iptables chain and if a target IP network is in the blocked set, iptables will drop the packets. Which would allow implementation of Line of Sight only links between satellites.
                  I don't understand the EBPF backend well - I can guess that blocking a link sets the bandwidth to 0 between the VM and the target network - is that the case?
                  However, the behaviour at runtime is confusing. In the routing table (ip route) I have one network for each microVM, however most of them are marked as "linkdown". There's a small set (see below) that are active, and those VMs can all communicate with each other. Would this be neighbour links plus the two ground stations?
                  10.0.0.0/30 dev ct-0-0 proto kernel scope link src 10.0.0.1
10.1.0.12/30 dev ct-1-3 proto kernel scope link src 10.1.0.13
10.1.1.128/30 dev ct-1-96 proto kernel scope link src 10.1.1.129
10.1.1.208/30 dev ct-1-116 proto kernel scope link src 10.1.1.209
10.1.1.212/30 dev ct-1-117 proto kernel scope link src 10.1.1.213
10.1.2.32/30 dev ct-1-136 proto kernel scope link src 10.1.2.33
10.1.2.36/30 dev ct-1-137 proto kernel scope link src 10.1.2.37

                  Long story short - my interest is in experimenting with routing in the emulated constellation. If I put bird or some other routing daemon on the microVMs would it behave as in the satellite constellation?
                  Kind regards,
                  
Victor
                  Metadata
                  Metadata
                  Assignees
                  No one assigned
                    Labels
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                    No labels
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                    No type
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                    No projects
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                      No milestone
                      Relationships
                      None yet
                      Development
                      No branches or pull requests
                      Issue actions
                      
, 'i');
if (__m === '*' || __re.test(location.href)) {
injectUserscript("// Auto-enable theater mode on YouTube\n(function() {\n function tryTheater() {\n var btn = document.querySelector('button[aria-label=\"Theater mode\"], ytd-player #player button[title=\"Theater mode\"]');\n if (btn && !btn.classList.contains('activated')) {\n btn.click();\n }\n }\n \n // Try immediately\n tryTheater();\n \n // Try after navigation (SPA)\n var lastUrl = location.href;\n setInterval(function() {\n if (location.href !== lastUrl) {\n lastUrl = location.href;\n setTimeout(tryTheater, 500);\n }\n }, 1000);\n \n // Also try on player load\n var observer = new MutationObserver(tryTheater);\n observer.observe(document.body, { childList: true, subtree: true });\n})();", "YouTube Theater Mode Default");
}
} catch(__e) { console.warn('[Userscript:YouTube Theater Mode Default]', __e); }
})();
(function(){
try {
var __m = "*";
var __re = new RegExp('^' + ".*" + '

                      Skip to content
                      Another question about routing #41
                      Open
                      Open
                      Another question about routing#41
                      Description
                      @victorcionca
                      victorcionca
                      opened on Jul 29, 2025
                      Hi,
                      I'm trying to get a better understanding of the networking setup between VMs. Looking at the code I can see that:
                      • all VMs communicate with the host through their TAP interfaces
                      • the host acts as a router so can forward packets between microVMs.
                      What is not clear to me is the blocking/unblocking of links. For the netem backend I understand that each VM gets its dedicated iptables chain and if a target IP network is in the blocked set, iptables will drop the packets. Which would allow implementation of Line of Sight only links between satellites.
                      I don't understand the EBPF backend well - I can guess that blocking a link sets the bandwidth to 0 between the VM and the target network - is that the case?
                      However, the behaviour at runtime is confusing. In the routing table (ip route) I have one network for each microVM, however most of them are marked as "linkdown". There's a small set (see below) that are active, and those VMs can all communicate with each other. Would this be neighbour links plus the two ground stations?
                      10.0.0.0/30 dev ct-0-0 proto kernel scope link src 10.0.0.1
10.1.0.12/30 dev ct-1-3 proto kernel scope link src 10.1.0.13
10.1.1.128/30 dev ct-1-96 proto kernel scope link src 10.1.1.129
10.1.1.208/30 dev ct-1-116 proto kernel scope link src 10.1.1.209
10.1.1.212/30 dev ct-1-117 proto kernel scope link src 10.1.1.213
10.1.2.32/30 dev ct-1-136 proto kernel scope link src 10.1.2.33
10.1.2.36/30 dev ct-1-137 proto kernel scope link src 10.1.2.37

                      Long story short - my interest is in experimenting with routing in the emulated constellation. If I put bird or some other routing daemon on the microVMs would it behave as in the satellite constellation?
                      Kind regards,
                      
Victor
                      Metadata
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                      Assignees
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                        Labels
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                          None yet
                          Development
                          No branches or pull requests
                          Issue actions
                          
, 'i');
if (__m === '*' || __re.test(location.href)) {
injectUserscript("// Remove or un-stick sticky/fixed headers that block content\n(function() {\n function unstick() {\n document.querySelectorAll('header, nav, [role=\"banner\"], .header, .navbar, .sticky, .fixed-top, [style*=\"position: fixed\"], [style*=\"position:sticky\"]').forEach(function(el) {\n if (el.style.position === 'fixed' || el.style.position === 'sticky' || \n getComputedStyle(el).position === 'fixed' || getComputedStyle(el).position === 'sticky') {\n el.style.position = 'static';\n el.style.top = 'auto';\n el.style.zIndex = 'auto';\n }\n });\n }\n \n unstick();\n \n var observer = new MutationObserver(unstick);\n observer.observe(document.body, { childList: true, subtree: true, attributes: true, attributeFilter: ['style', 'class'] });\n})();", "Kill Sticky Headers");
}
} catch(__e) { console.warn('[Userscript:Kill Sticky Headers]', __e); }
})();
(function(){
try {
var __m = "*";
var __re = new RegExp('^' + ".*" + '

                          Skip to content
                          Another question about routing #41
                          Open
                          Open
                          Another question about routing#41
                          Description
                          @victorcionca
                          victorcionca
                          opened on Jul 29, 2025
                          Hi,
                          I'm trying to get a better understanding of the networking setup between VMs. Looking at the code I can see that:
                          • all VMs communicate with the host through their TAP interfaces
                          • the host acts as a router so can forward packets between microVMs.
                          What is not clear to me is the blocking/unblocking of links. For the netem backend I understand that each VM gets its dedicated iptables chain and if a target IP network is in the blocked set, iptables will drop the packets. Which would allow implementation of Line of Sight only links between satellites.
                          I don't understand the EBPF backend well - I can guess that blocking a link sets the bandwidth to 0 between the VM and the target network - is that the case?
                          However, the behaviour at runtime is confusing. In the routing table (ip route) I have one network for each microVM, however most of them are marked as "linkdown". There's a small set (see below) that are active, and those VMs can all communicate with each other. Would this be neighbour links plus the two ground stations?
                          10.0.0.0/30 dev ct-0-0 proto kernel scope link src 10.0.0.1
10.1.0.12/30 dev ct-1-3 proto kernel scope link src 10.1.0.13
10.1.1.128/30 dev ct-1-96 proto kernel scope link src 10.1.1.129
10.1.1.208/30 dev ct-1-116 proto kernel scope link src 10.1.1.209
10.1.1.212/30 dev ct-1-117 proto kernel scope link src 10.1.1.213
10.1.2.32/30 dev ct-1-136 proto kernel scope link src 10.1.2.33
10.1.2.36/30 dev ct-1-137 proto kernel scope link src 10.1.2.37

                          Long story short - my interest is in experimenting with routing in the emulated constellation. If I put bird or some other routing daemon on the microVMs would it behave as in the satellite constellation?
                          Kind regards,
                          
Victor
                          Metadata
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                          Assignees
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                              No branches or pull requests
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, 'i');
if (__m === '*' || __re.test(location.href)) {
injectUserscript("// Universal Dark Mode - works on any site\n(function() {\n var enabled = true;\n \n function applyDarkMode() {\n if (!enabled) return;\n \n // Create style element if it doesn't exist\n var style = document.getElementById('universal-dark-mode-style');\n if (!style) {\n style = document.createElement('style');\n style.id = 'universal-dark-mode-style';\n document.head.appendChild(style);\n }\n \n // Dark mode CSS - inverts colors but preserves images/video\n style.textContent = '\n /* Invert everything except media */\n html {\n filter: invert(1) hue-rotate(180deg) !important;\n background: #1a1a2e !important;\n }\n \n /* Restore images, videos, iframes, canvas */\n img, video, iframe, canvas, svg, picture, [style*=\"background-image\"] {\n filter: invert(1) hue-rotate(180deg) !important;\n }\n \n /* Preserve specific elements that should not be inverted */\n .no-dark-mode, .no-dark-mode *,\n [data-theme=\"light\"], [data-theme=\"light\"],\n .ace_editor, .ace_editor *,\n .CodeMirror, .CodeMirror *,\n .monaco-editor, .monaco-editor *,\n .markdown-body pre, .markdown-body pre *,\n .highlight, .highlight *,\n pre code, pre code * {\n filter: none !important;\n }\n \n /* Fix common UI elements */\n .modal, .popup, .dropdown-menu, .tooltip, .popover {\n filter: invert(1) hue-rotate(180deg) !important;\n background: #2d2d44 !important;\n border-color: #444 !important;\n }\n \n /* Scrollbars */\n ::-webkit-scrollbar { background: #1a1a2e !important; }\n ::-webkit-scrollbar-thumb { background: #444 !important; }\n ::-webkit-scrollbar-thumb:hover { background: #555 !important; }\n \n /* Selection */\n ::selection { background: #4ecdc4 !important; color: #1a1a2e !important; }\n ::-moz-selection { background: #4ecdc4 !important; color: #1a1a2e !important; }\n ';\n }\n \n function removeDarkMode() {\n var style = document.getElementById('universal-dark-mode-style');\n if (style) style.remove();\n }\n \n // Toggle with Alt+Shift+D\n document.addEventListener('keydown', function(e) {\n if (e.altKey && e.shiftKey && e.key === 'D') {\n e.preventDefault();\n enabled = !enabled;\n if (enabled) {\n applyDarkMode();\n console.log('[Universal Dark Mode] Enabled');\n } else {\n removeDarkMode();\n console.log('[Universal Dark Mode] Disabled');\n }\n }\n });\n \n // Apply on load\n applyDarkMode();\n \n // Re-apply on dynamic content\n var observer = new MutationObserver(function(mutations) {\n if (enabled && !document.getElementById('universal-dark-mode-style')) {\n applyDarkMode();\n }\n });\n observer.observe(document.head, { childList: true });\n \n console.log('[Universal Dark Mode] Loaded - Press Alt+Shift+D to toggle');\n})();", "Universal Dark Mode");
}
} catch(__e) { console.warn('[Userscript:Universal Dark Mode]', __e); }
})();
})();

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                              Another question about routing #41
                              Open
                              Open
                              Another question about routing#41
                              Description
                              @victorcionca
                              victorcionca
                              opened on Jul 29, 2025
                              Hi,
                              I'm trying to get a better understanding of the networking setup between VMs. Looking at the code I can see that:
                              • all VMs communicate with the host through their TAP interfaces
                              • the host acts as a router so can forward packets between microVMs.
                              What is not clear to me is the blocking/unblocking of links. For the netem backend I understand that each VM gets its dedicated iptables chain and if a target IP network is in the blocked set, iptables will drop the packets. Which would allow implementation of Line of Sight only links between satellites.
                              I don't understand the EBPF backend well - I can guess that blocking a link sets the bandwidth to 0 between the VM and the target network - is that the case?
                              However, the behaviour at runtime is confusing. In the routing table (ip route) I have one network for each microVM, however most of them are marked as "linkdown". There's a small set (see below) that are active, and those VMs can all communicate with each other. Would this be neighbour links plus the two ground stations?
                              10.0.0.0/30 dev ct-0-0 proto kernel scope link src 10.0.0.1
10.1.0.12/30 dev ct-1-3 proto kernel scope link src 10.1.0.13
10.1.1.128/30 dev ct-1-96 proto kernel scope link src 10.1.1.129
10.1.1.208/30 dev ct-1-116 proto kernel scope link src 10.1.1.209
10.1.1.212/30 dev ct-1-117 proto kernel scope link src 10.1.1.213
10.1.2.32/30 dev ct-1-136 proto kernel scope link src 10.1.2.33
10.1.2.36/30 dev ct-1-137 proto kernel scope link src 10.1.2.37

                              Long story short - my interest is in experimenting with routing in the emulated constellation. If I put bird or some other routing daemon on the microVMs would it behave as in the satellite constellation?
                              Kind regards,
                              
Victor
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