執行個體核心會發出 ARP 要求，而虛擬私有雲網路會發出 ARP 回覆。MAC 位址與 IP 位址之間的對應關係由執行個體核心處理。
MAC 對照表、IP 對照表、有效連線表
這些表格託管在基礎虛擬私有雲網路上，而且無法進行檢查或設定。
DNS 伺服器
每個執行個體的中繼資料伺服器可做為 DNS 伺服器使用。DNS 伺服器會儲存本機虛擬私人雲端網路中所有虛擬私人雲端網路 IP 位址的 DNS 項目，並呼叫 Google 的公開 DNS 伺服器，取得虛擬私人雲端網路外的項目。您無法設定這個 DNS 伺服器。系統會設定每個執行個體上的 DHCP 用戶端，以管理執行個體的 /etc/resolv.conf 檔案。
您可以修改 DHCP 政策，將自己的搜尋網域或網域名稱伺服器新增至執行個體的 /etc/resolv.conf。許多 Linux 發行版允許透過 /etc/dhcp/dhclient.conf 保留這些修改內容。詳情請參閱內部 DNS 說明文件。
虛擬私人雲端網路與外部之間的封包處理
進出虛擬私人雲端網路的封包是透過網路代碼進行處理，網路代碼會根據防火牆規則、外部 IP 對照表和有效連線表來檢查封包。虛擬私人雲端網路也會在進出虛擬私人雲端網路的封包上執行 NAT。
[[["容易理解","easyToUnderstand","thumb-up"],["確實解決了我的問題","solvedMyProblem","thumb-up"],["其他","otherUp","thumb-up"]],[["難以理解","hardToUnderstand","thumb-down"],["資訊或程式碼範例有誤","incorrectInformationOrSampleCode","thumb-down"],["缺少我需要的資訊/範例","missingTheInformationSamplesINeed","thumb-down"],["翻譯問題","translationIssue","thumb-down"],["其他","otherDown","thumb-down"]],["上次更新時間：2025-09-05 (世界標準時間)。"],[],[],null,["# Advanced VPC concepts\n=====================\n\nThis page goes into additional detail about Virtual Private Cloud (VPC) networks.\nBefore reading this page, see [VPC networks](/vpc/docs/vpc). If you are interested in peered VPC networks, see [VPC Network Peering](/vpc/docs/vpc-peering).\n\nLow-level VPC networking details\n--------------------------------\n\nThis section provides some low-level VPC networking details.\nYou do not need to read this for typical usage, but it provides more\ninsight about how VPC networking works. The following\ndiagram describes these low-level details, with more information in the\ncorresponding sections.\n[](/static/vpc/images/detailednetworkingdiagram.svg) The VPC network (click to enlarge).\n\n### Who handles what\n\nThe different VPC networking features are handled by\ndifferent parts of the system. Some of these are standard networking\nfeatures that are well documented, and some of them are specific to\nVPC networks. Some features you can configure, and some you cannot.\nVPC networks use Linux's\n[VIRTIO network module](http://dl.acm.org/citation.cfm?id=1400097.1400108)\nto model Ethernet card and router functionality, but higher levels of the\nnetworking stack, such as ARP lookups, are handled using standard networking\nsoftware.\n\nARP lookup\n: The instance kernel issues\n [ARP requests](https://wikipedia.org/wiki/Address_Resolution_Protocol)\n and the VPC network issues ARP replies. The mapping between MAC addresses and IP addresses\n is handled by the instance kernel.\n\nMAC lookup table, IP lookup table, active connection table\n: These tables are hosted on the underlying VPC network and cannot be inspected or\n configured.\n\nDNS server\n\n: Each instance's metadata server acts as a DNS server. It stores the DNS\n entries for all VPC network IP addresses in the local VPC network and calls\n Google's public DNS server for entries outside the VPC network. You cannot\n configure this DNS server. The DHCP client on each instance is configured to\n manage the instance's `/etc/resolv.conf` file.\n\n: You can add your own search domain or nameservers to the instance's\n `/etc/resolv.conf` by modifying the DHCP policy. Many Linux\n distributions allow these modifications to persist via\n [`/etc/dhcp/dhclient.conf`](https://www.isc.org/wp-content/uploads/2017/08/dhcp41clientconf.html).\n See the [Internal DNS](/compute/docs/internal-dns) documentation for more\n information.\n\nPacket handling between the VPC network and the outside\n\n: Packets coming into or out of the VPC network are handled by network code that\n examines the packet against firewall rules, against the external IP lookup table, and\n against the active connections table. The VPC network also performs NAT on packets\n coming into and out of the VPC network.\n\nPackets received by an instance\n\n: These packets are received and turned into a stream by the instance kernel in\n the standard fashion.\n\nPackets sent by an instance\n\n: Packets are sent by the instance kernel in the standard way. Interface\n and network functionality are modeled using the\n [VIRTIO network module](http://dl.acm.org/citation.cfm?id=1400097.1400108).\n\n### Detailed connection walkthroughs\n\nHere are more details about what happens when an instance makes a VPC\nnetwork call.\n\n**An instance makes a call:**\n\n1. If the target address is an instance name or a URL such as www.google.com, the instance calls the DNS service on its metadata server and gets back the matching IP address. You can configure your instance to consult another DNS service, but then you will not be able to resolve instance names.\n2. The destination IP address is examined against the subnet's IP address range,\n which every instance knows.\n\n 1. If the IP address is not in the\n current VPC network or in a VPC network\n peered using VPC Network Peering:\n\n 1. The instance sends the packet to the subnet's gateway MAC address\n with the destination set to the packet's final destination. The\n instance might need to make an ARP request to resolve the gateway's\n MAC address.\n\n 2. The VPC network\n rewrites the IP header to declare the instance's external IP address\n as the source. If the instance has no external IP address, the call\n is not allowed, and the VPC network drops the packet without informing\n the sender.\n\n 3. The VPC network records the outgoing packet and adds the source and\n destination to the active connections table.\n\n 4. The VPC network sends the packet on to its destination.\n\n 5. The destination gets the packet and responds if it chooses.\n\n 6. The VPC network receives the response, consults the active connections\n table, notes that this is an active connection, and allows it. The\n VPC network consults its network/external IP lookup table and replaces\n the instance's external IP address with the matching network\n address and sends the packet to the source instance.\n\n 7. The instance receives the packet.\n\n 2. If the destination IP address is within the VPC network\n or in a VPC network peered using VPC Network Peering:\n\n 1. The instance is configured with an IP with 255.255.255.255 mask,\n so the instance sends the packet to the subnet's gateway\n MAC address. The instance first might need to make an ARP request\n to resolve the gateway's MAC address.\n\n 2. Google Cloud forwards the packet to the destination IP address\n within the current or peered VPC network.\n\n 3. The target instance receives the packet. The target instance\n checks ingress firewall to determine if the packet is allowed. If\n not, the packet is dropped silently. Otherwise, the instance\n processes the packet.\n\n**An external instance or computer calls an instance:**\n\n1. The external caller sends a packet to an instance's external IP address, which\n is owned by the VPC network.\n\n2. The VPC network compares the packet against the active connections table to\n see whether this is an existing connection:\n\n 1. If it is not an existing connection, the VPC network looks for a firewall rule to allow the connection.\n 2. If there is no firewall rule, the VPC network drops the packet without informing the sender.\n3. If there is an existing connection or valid firewall rule, the VPC network examines\n its lookup table and replaces the external IP with the corresponding internal\n IP in the packet, logs the incoming packet in the active connections table,\n and sends the packet to the target instance.\n\n4. The instance receives the packet and responds as described in\n **[If the IP address is outside the VPC network IP range](#ip_outside_network)**\n when sending a packet outside the network range.\n\n5. The VPC network receives the reply, finds the matching incoming request in the\n active connections table, and allows the packet through. Before sending, it\n modifies the source IP address by replacing the instance's internal IP with\n the corresponding external IP from its lookup table.\n\nMeasure VPC network throughput\n------------------------------\n\nFor instructions, see\n[Calculate network throughput](/community/tutorials/network-throughput).\n\nWhat's next\n-----------\n\n- To learn about VPC networks, see [VPC networks](/vpc/docs/vpc).\n- To create, modify, and delete VPC networks, see [Create and manage VPC networks](/vpc/docs/create-modify-vpc-networks)."]]
