I have 2 AWS instances, i-1 and i-2. They are each on a different security group: sg-1 and sg-2, respectively. Both machines have elastic IPs.
sg-2 is configured to allow all traffic from sg-1, regardless of port, source IP or protocol.
When i-1 tries to talk to i-2 its traffic is being blocked. It seems AWS doesn't account for the fact that i-1's traffic is actually coming from its elastic IP.
Is this expected? Is there anything I can do to work around it, apart from manually adding i-1's elastic IP to sg-2?
sg-2 is configured to allow all traffic from sg-1
When you do this, only traffic from Private IP address is allowed. However, as you as using EIP, you explicitly need to allow traffic from that ip address.
Read this: https://forums.aws.amazon.com/thread.jspa?messageID=414060
Quoting from above link:
Out of curiosity, are you perhaps connecting using a public IP address? When you use a rule with a security group as the source, it will only match when connecting over the internal network. The private IP address can change though. If you have an Elastic IP associated with the instance, the public DNS name happens to be static and will always resolve to the current private IP address when used from within the same EC2 region. That allows you to easily connect internally without worrying about any address changes.
You haven't really provided enough information to diagnose the problem, but there are a few things to check:
Is I-1 definitely in SG-1? If you've got the instances muddled, the SG rules would be around the wrong way.
Does the machine in SG-2 have a firewall running that might be blocking incoming traffic even though the SG rules are allowing it?
You've tagged this with the VPC tag - do you have any network ACL settings that might be preventing traffic flow? Are the machines private, using a NAT appliance to get out to the Internet, or public, routing through the standard AWS gateway? Can I-1 see the Internet? If you're routing through a NAT, assigning an EIP to a machine effectively cuts it off from the Internet because EIP and NAT are mutually incompatible, and although I haven't tried it this might also screw up SG routing.
Does SG-1 have any egress rules that might be preventing traffic from leaving?
The answer to your question is likely to be found in the resolution of one of these questions if the answer to any of them is 'Yes'.
As previously stated by slayedbylucifer, you will need to explicitly allow traffic from the EIP.
Here's the reasoning from the official AWS documentation about Security Groups:
When you specify a security group as the source for a rule, traffic is allowed from the network interfaces that are associated with the source security group for the specified protocol and port. Incoming traffic is allowed based on the private IP addresses of the network interfaces that are associated with the source security group (and not the public IP or Elastic IP addresses).
Related
I am new to AWS that's why, I am asking this question. Is it possible in AWS network firewall to only allow the incoming traffic from outside that comes from a particular DNS. According to my knowledge, it's easily possible with IP address but the problem is that the IP address of the source does not remain same and is dynamic. I have also read in various posts that in security groups we also can not mention DNS and we can only mention IP addresses. I have also read that in AWS network firewall, it's also possible to block traffic for a particular domain that's generated from EC2 instance using firewall but is it possible the other way around? Is it possible to only allow the traffic of the particular DNS that's coming from the Internet gateway to the VPC using AWS network firewall. Can anyone guide me in this regard?
We are using a shared VPC with two subnets (10.65.0.0/16 and 10.66.0.0/16). The shared VPC has connection to on-prem network, so both two subnets can access the resource hosted on on-prem. Since we use one subnet for DEV environment, and the other one for PROD environment, we want to block all traffic between those two subnets. I don't want to manage those firewall rules by using tags or service accounts of each instance hosting on those subnets, since the owner of all projects hosting in those two subnets may not always following the rules, and cause extra communications to clarify. Ideally, I want to create some firewall rules to block the traffic just using those two IP ranges of subnets. To isolate subnets between each other, I need to create a "deny" firewall rule with source "10.65.0.0/16" and distinction "10.66.0.0/16", and another one with source "10.66.0.0/16" and distinction "10.65.0.0/16". For what I saw, in both egress and ingress firewalls, it's only allowed to set IP ranges on either source or distinction, but cannot be both. It looks there is no way to set both source and distinction in a single firewall using CIDR.
I know using peered network can easily cut the traffic between VPCs/subnets. But there is limitation in VPC, that the routing between 2+ layers of peering are terrible, and resources managed by google already involved a layer of peering, so if possible I don't want to involve another layer of peered network. If there are no better ideas, I probably have to use either Tags or Service accounts to create firewalls one by one.
Please share your ideas, or any other way to resolve my problem.
Thank you
Consulted Google tech support for this question. Their suggestion is no surprise. It can not be done by setting source IP CIDR and distinction CIDR. Their suggestion is using "Tags" + "resource IP ranges".
e.g. - allow all [ingress], Targets tags: vmGroup-1, Source IPv4 : CIDR of vmGroup-1
Basically, going through this way instead of create "deny" firewalls caused by one advantage of VPC, and one limitation of VPC. The advantage is: The advantage is: In VPC the traffic is blocked between any instances naturally, even they are in the same subnet, firewalls are created in VPC but working on each instance individually, it's like each instance has its own firewall. The limitation is: so far, VPC don't allow firewall be created with both source and distinction IP ranges be defined.
2 questions on NLB in AWS
I have a requirement to use NLB in front of the EC2 which runs MYSQL. This EC2 is in private network. I just want to allow NLB to be accessed by some particular internet IP. If it's ALB, I can use security group to do this. However, without security group in NLB, how can I achieve this?
In this setup, I connect to NLB from my PC and reach to that MYSQL EC2. To make it success, I find that I have to allow 0.0.0.0/0 in the incoming rule of the EC2 security group instead of just putting my PC IP. I thought my PC IP should be brought to EC2 directly through NLB. Is it not true? I dont want to allow 0.0.0.0/0 in EC2 security group. Is there any better way?
Thanks!
The security group evaluations are performed by the instances security groups for the Network Load Balancer. You would need to add the IP addresses you would like to communicate with the NLB to your instances, as long as your instance is in a private subnet this will prevent any client directly interacting with the host.
Network Load Balancers do not have associated security groups. Therefore, the security groups for your targets must use IP addresses to allow traffic from the load balancer.
More information is available in the Register targets with your target group documentation.
The only way to block the traffic in your case is to have the IPs to which you want to allow access in the EC2 SG.
However you need to account for the fact that there is a difference on the IP address from which the request will come from and thus will be evaluated from the EC2 SG based on how you have configured the target group of the NLB and more specifically on whether you have set up the target type to be instance or ip, as there is a difference in the NLB behaviour.
If the target type is set to instance, the NLB will pass the traffic to your instance as is, and the EC2 SG will see your locap PC public IP address, and if there is a rule to allow it you will be able to connect
If the target type is set to ip, the NLB is doing an NAT, and the EC2 SG will actually see the private IP of the NLB as a source IP for the incoming traffic.
Take a look at the Source IP Preservation in the NLB Target Group documentation.
There is a similar discussion in this question.
I was able to connect my private Ec2 instance to the internet through NAT instance.
wget google.com was successful.
But when I attached a NACL to my private subnet.I wasn't able to connect to the internet.Can anyone please tell me what is wrong with my NACL.
10.0.1.0/24 and 10.0.2.0/24 are CIDRs of public subnet(which has the NAT instance)
private NACL inbound rule
private NACL outbound rule
Also, when I add rule to accept all traffic from internet.It works. Is it correct practice to add this rule ?
Based on the comments.
The issue was due to blocking inbound internet traffic (0.0.0.0/0). From the Instances cannot access the internet in AWS docs, to enable internet access of the instance using NAT, the following must be ensured:
Ensure that the network ACLs that are associated with the private subnet and public subnets do not have rules that block inbound or outbound internet traffic. For the ping command to work, the rules must also allow inbound and outbound ICMP traffic.
Question from comments:
But just one question how will whitelisting work in this case. If I only want to download certain libraries using the internet and not allow any api requests ?
If you know IP ranges of the public servers that these libraries are going to be downloaded from, then you could limit the internet traffic to only these ranges. But if the range is not fixed or unknown you have to allow all (0.0.0.0/0) internet traffic in the rules.
Generally, security groups are used as primary way of controlling network traffic. NACLs are good due to their their denying ability. Security groups can't explicitly deny traffic, thus NACLs are helpful in cases where you want to explicitly deny some IPs. But in your case, you are allow only traffic. Thus I think the use of default NACLs would be sufficient and could be considered.
Has someone configured a NLB in the public subnets of your VPC to route traffic to EC2 instances that are in the private subnets?
When using an ELB, a good solution is to create a Security Group for the ELB and then create another SecurityGroup for the private EC2 Instances, allowing incoming traffic from that ELB Security Group, as explained here:
https://aws.amazon.com/premiumsupport/knowledge-center/public-load-balancer-private-ec2/
"You can also add a rule on the instance’s security group to allow traffic from the security group assigned to the load balancer. For example, if the security group on the load balancer is sg-1234567a, make the following changes on the security group associated with the private instances"
Since you cannot associate a Security Group to a NLB, how could you accomplish this with the same type of security?
Thanks!
Since you cannot associate a Security Group to a NLB, how could you
accomplish this with the same type of security?
The security aspect does not change.
NLB is a different beast, it not the same as classic Load Balancers. For Classic Load Balancers, from the point of view of your instances, traffic does appear to come from inside the VPC. From outside, traffic goes to a (random and mutating) list of IP addresses, resolved by the DNS record that AWS provides to you.
Network Load Balancers are completely different. From the point of view of your instances, they are completely invisible. If it is an external network load balancer, traffic appears to be coming from instances on the internet directly (even though this is an illusion). Therefore, if you want to talk to everyone on the internet, 0.0.0.0/0 is what you open it to.
This is, in fact, what the documentation says:
https://docs.aws.amazon.com/elasticloadbalancing/latest/network/target-group-register-targets.html#target-security-groups
Recommended Rules
Inbound Source Port Range Comment
Client IP addresses instance listener Allow traffic from clients on the instance listener port
VPC CIDR health check Allow traffic from the load balancer on the health check port
Client IP addresses is whatever your client IPs are. If they are on the open internet, 0.0.0.0/0 it is. Adding the NLB private IP address, as I saw in other responses, accomplishes nothing. Traffic is not coming from there, as far as the instances are concerned.
On the security angle, nothing changes. Since your instances are in private subnets, traffic cannot flow directly to them, as there is a NAT gateway in the middle. It can only flow from them to the internet (through NAT gateway, then internet gateway). Even if you specify all traffic is allowed from everywhere, traffic still won't come. It will have to come through another way. In your case, that way is the NLB, which has a fixed number of ports it listens to, and only sends traffic to the destination ports on the instances you specify.
If you are moving from classic Load Balancers to NLBs, move the security group rules from the Load Balancer to your instances. Or better yet, since you can have multiple security groups, just add the SG you currently have for the classic LB to the instances(and update any ASGs as needed). Your security posture will be exactly the same. With the added benefit that now your applications won't need things like proxy protocol to figure out where traffic is coming from, it is no longer obfuscated by the load balancer.
That is indeed true as per AWS Documentation :
Network Load Balancers do not have associated security groups.
Therefore, the security groups for your targets must use IP addresses
to allow traffic from the load balancer.
So If you do not want to grant access to the entire VPC CIDR, you can grant access to the private IP addresses used by the load balancer nodes. There is one IP address per load balancer subnet.
On NLB Tab of there is one Network Interface per Load Balancer from there :
On the Details tab for each network interface, copy the address from
Primary private IPv4 IP.
You can use this private IP Address at add it SG of EC2 Instances.
Please Refer to AWS Documentation
Tail your http access logs and you will see there is no changing of source IP address from the network load balancer which means you need to allow 0.0.0.0/0 on the endpoints security group if the internet needs access to your endpoint.
This is only ok if you use a private subnet so be careful if you have this server on a public subnet as this solution would not be advisable. In this case just use an application load balancer. You can still setup the same listener and configure a target group by instance as well. The application load balancer will update the source IP address to it's own private address if you tail the access logs. The advantage of this is you only need to allow https traffic to the app load balancer and then you can accept http for the target group if you like from the load balancer.