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Module 1: It Helps To Network

    Study Reminders
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    Routes and Firewall Rules in the Cloud
    In this topic you will consider routes and how firewall rules allow traffic to flow within a VPC. By default every network has routes that let instances in a network send traffic directly to each other even across subnets. In addition every network has a default route that directs Packets to destinations that are outside the network although these routes cover most normal routing needs you can also create special routes that override these routes, just creating a route doesn’t ensure that packets will be received by the specified next half firewall rules must also allow the packet. The default network as a pre-configured firewall rules that allow all instances in the network to talk with each other. Manually created networks don’t have such rules so you must create them as you will experience in the first lap. Rounds much packets by destination IP address however no traffic will flow without also matching a firewall rule. Around the screen is created when the network is created enabling traffic delivery from anywhere also a route is created when a subnet is created this is what enables vms on the same network to communicate. This diagram shows a simplified routing table but you will look at this in more detail next. Each route in the routes collection can apply to one or more instances a route applies to an instance if the network and instance tags match if the network matches and there are no instance tags specified the role applies to all instances in that network. Compute engine then uses the routes collection to create individual read-only routing tables for each instance. This diagram shows a massively scalable virtual router at the core of each network every virtual machine instance in the network is directly connected to the router and packets living a virtual machine instance are first handled at this layer before they are forwarded to the next half. The virtual network router selects the next half for a packet by consulting the routing table for that instance. Every route consist of a destination and a next top, traffic whose destination IP is within the destination range is sent to the next route for delivery. GCP firewall rules protect virtual machine instances from un approved connections both inbound and outbound known as ingress and egress respectively. essentially every VPC network functions as a distributor firewall. Although firewall rules are applied to the network as a whole connections are allowed or denied at the instance level, you can think of the firewall as existing not only between your instances and other networks on between individual instances within the same network. GCP firewall rules are stateful this means that if a connection has allowed between a source and target or target and destination all subsequent traffic in either direction will be allowed in other words firewall rules allow bidirectional communication once a session is established, also if for some reason all firewall rules in a network are deleted there is still an implied deny all ingress rule and an implied allow all egress rule for the network. You should Express your desired firewall configuration as a set of firewall rules, conceptually a firewall rule is composed of certain parameters the direction of the rule inbound connection are matched against ingress rules only and outbound connections are matched against egress rules only, for the ingress direction sources can be specified as part of the rule with IP addresses source tags or a source service account for the egress direction destination can be specified as part of the rule with one or more ranges of IP addresses. The protocol and port of the connection where any rule can be restricted to apply to specific protocols only or specific combinations of protocol and ports only. The action of the rule which is to allow or deny packets that match the direction for the carport and source or destination of the rule. The priority of the rule which go once the order in which the rules are evaluated the first matching rule is applied and lastly the rule assignment by default all rules are assigned to all instances but you can assign some rules to certain instances only. Let’s look at some gcp firewall use cases for both egress and ingress, Engress firewall rules control outgoing connections that originated inside your gcp networks. Egress allow rules allow outbound connections that match specific protocol force and IP addresses. Egress deny rules prevent instances from initiating connections that match non permitted ports, protocol and IP range combinations. For egress firewall rules destinations to which a rule applies may be specified using IP CIDR Rangesspecifically you can use destination range to protect from undesired connections initiated by a VM instance towards an external destination for example and external host, you can also use destination Ranges to protect from undesired connections initiated by a vm instance toward specific gcp cidr ranges for example of vm in a specific subnet. Ingress firewall rules protect against incoming connections to the instance from any source ingress allow rules allow specific protocol, ports and IP addresses to connect in the firewall prevents instances from receiving connections on non-permitted ports or protocols rules can be restricted to only affect particular sources. Source CIDR ranges can be used to protect an instance from undesired connections coming either from external network or from GCP IP ranges this diagram illustrates A VM receiving a connection from an external address and another Vm receiving connection from a VM in the same network. You can control ingress connections from a VM instance by constructing inbound connection conditions using a source CIDR Ranges, protocols or ports