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| title | sort_key |
|---|---|
| Connecting To The Network | B |
The default behaviour for Geth is to connect to Ethereum Mainnet. However, Geth can also connect to public testnets, private networks and local testnets. Command line flags are provided for connecting to the popular public testnets:
--ropsten, Ropsten proof-of-work test network--rinkeby, Rinkeby proof-of-authority test network--goerli, Goerli proof-of-authority test network--sepoliaSepolia proof-of-work test network
Providing these flags at startup instructs Geth to connect to the specific public testnet instead of Ethereum Mainnet. Because these are public testnets that have been running for several years, Geth has to download the historical blockchain data from genesis, just the same as for Ethereum Mainnet.
Note: network selection is not persisted in the config file. To connect to a pre-defined network you must always enable it explicitly, even when using the --config flag to load other configuration values. For example:
# Generate desired config file. You must specify testnet here.
geth --goerli --syncmode "full" ... dumpconfig > goerli.toml
# Start geth with given config file. Here too the testnet must be specified.
geth --goerli --config goerli.toml
Finding peers
Geth continuously attempts to connect to other nodes on the network until it has enough peers. If UPnP (Universal Plug and Play) is enabled at the router or Ethereum is run on an Internet-facing server, it will also accept connections from other nodes. Geth finds peers using the discovery protocol. In the discovery protocol, nodes exchange connectivity details and then establish sessions (RLPx). If the nodes support compatible sub-protocols they can start exchanging Ethereum data on the wire.
A new node entering the network for the first time gets introduced to a set of peers by a bootstrap node ("bootnode") whose sole purpose is to connect new nodes to peers. The endpoints for these bootnodes are hardcoded into Geth, but they can also be specified by providing the --bootnode flag along with comma-separated bootnode addresses in the form of enodes on startup. For example:
geth --bootnodes enode://pubkey1@ip1:port1,enode://pubkey2@ip2:port2,enode://pubkey3@ip3:port3
There are scenarios where disabling the discovery process is useful, for example for running a local test node or an experimental test network with known, fixed nodes. This can be achieved by passing the --nodiscover flag to Geth at startup.
Connectivity problems
There are occasions when Geth simply fails to connect to peers. The common reasons for this are:
-
Local time might be incorrect. An accurate clock is required to participate in the Ethereum network. The local clock can be resynchronized using commands such as
sudo ntpdate -s time.nist.gov(this will vary depending on operating system). -
Some firewall configurations can prohibit UDP traffic. The static nodes feature or
admin.addPeer()on the console can be used to configure connections manually. -
Running Geth in light mode often leads to connectivity issues because there are few nodes running light servers. There is no easy fix for this except to switch Geth out of light mode.
-
The public test network Geth is connecting to might be deprecated or have a low number of active nodes that are hard to find. In this case, the best action is to switch to an alternative test network.
Checking Connectivity
The net module has two attributes that enable checking node connectivity from the interactive Javascript console. These are net.listening which reports whether the Geth node is listening for inbound requests, and peerCount which returns the number of active peers the node is connected to.
> net.listening
true
> net.peerCount
4
Functions in the admin module provide more information about the connected peers, including their IP address, port number, supported protocols etc. Calling admin.peers returns this information for all connected peers.
> admin.peers
[{
ID: 'a4de274d3a159e10c2c9a68c326511236381b84c9ec52e72ad732eb0b2b1a2277938f78593cdbe734e6002bf23114d434a085d260514ab336d4acdc312db671b',
Name: 'Geth/v0.9.14/linux/go1.4.2',
Caps: 'eth/60',
RemoteAddress: '5.9.150.40:30301',
LocalAddress: '192.168.0.28:39219'
}, {
ID: 'a979fb575495b8d6db44f750317d0f4622bf4c2aa3365d6af7c284339968eef29b69ad0dce72a4d8db5ebb4968de0e3bec910127f134779fbcb0cb6d3331163c',
Name: 'Geth/v0.9.15/linux/go1.4.2',
Caps: 'eth/60',
RemoteAddress: '52.16.188.185:30303',
LocalAddress: '192.168.0.28:50995'
}, {
ID: 'f6ba1f1d9241d48138136ccf5baa6c2c8b008435a1c2bd009ca52fb8edbbc991eba36376beaee9d45f16d5dcbf2ed0bc23006c505d57ffcf70921bd94aa7a172',
Name: 'pyethapp_dd52/v0.9.13/linux2/py2.7.9',
Caps: 'eth/60, p2p/3',
RemoteAddress: '144.76.62.101:30303',
LocalAddress: '192.168.0.28:40454'
}, {
ID: 'f4642fa65af50cfdea8fa7414a5def7bb7991478b768e296f5e4a54e8b995de102e0ceae2e826f293c481b5325f89be6d207b003382e18a8ecba66fbaf6416c0',
Name: '++eth/Zeppelin/Rascal/v0.9.14/Release/Darwin/clang/int',
Caps: 'eth/60, shh/2',
RemoteAddress: '129.16.191.64:30303',
LocalAddress: '192.168.0.28:39705'
} ]
The admin module also includes functions for gathering information about the local node rather than its peers. For example, admin.nodeInfo returns the name and connectivity details for the local node.
> admin.nodeInfo
{
Name: 'Geth/v0.9.14/darwin/go1.4.2',
NodeUrl: 'enode://3414c01c19aa75a34f2dbd2f8d0898dc79d6b219ad77f8155abf1a287ce2ba60f14998a3a98c0cf14915eabfdacf914a92b27a01769de18fa2d049dbf4c17694@[::]:30303',
NodeID: '3414c01c19aa75a34f2dbd2f8d0898dc79d6b219ad77f8155abf1a287ce2ba60f14998a3a98c0cf14915eabfdacf914a92b27a01769de18fa2d049dbf4c17694',
IP: '::',
DiscPort: 30303,
TCPPort: 30303,
Td: '2044952618444',
ListenAddr: '[::]:30303'
}
Custom Networks
It is often useful for developers to connect to private test networks rather than public testnets or Etheruem mainnet. These sandbox environments allow block creation without competing against other miners, easy minting of test ether and give freedom to break things without real-world consequences. A private network is started by providing a value to --networkid that is not used by any other existing public network (Chainlist) and creating a custom genesis.json file. Detailed instructions for this are available on the Private Networks page.
Static nodes
Geth also supports static nodes. Static nodes are specific peers that are always connected to. Geth reconnects to these peers automatically when it is restarted. Specific nodes are defined to be static nodes by saving their enode addresses to a json file which must be stored in datadir/geth/static-nodes.json. The content of static-nodes.json should be formatted as follows:
[
"enode://f4642fa65af50cfdea8fa7414a5def7bb7991478b768e296f5e4a54e8b995de102e0ceae2e826f293c481b5325f89be6d207b003382e18a8ecba66fbaf6416c0@33.4.2.1:30303",
"enode://pubkey@ip:port"
]
Static nodes can also be added at runtime in the Javascript console by passing an enode address to admin.addPeer():
admin.addPeer("enode://f4642fa65af50cfdea8fa7414a5def7bb7991478b768e296f5e4a54e8b995de102e0ceae2e826f293c481b5325f89be6d207b003382e18a8ecba66fbaf6416c0@33.4.2.1:30303")
Peer limit
It is sometimes desirable to cap the number of peers Geth will connect to in order to limit on the computational and bandwidth cost associated with running a node. By default, the limit is 50 peers, however, this can be updated by passing a value to --maxpeers:
geth <otherflags> --maxpeers 15
Trusted nodes
Geth supports trusted nodes that are always allowed to reconnect, even if the peer limit is reached. They can be added persistently via a config file <datadir>/geth/trusted-nodes.json or temporarily using the Javascript console. The format for the config file is identical to the one used for static nodes.
Nodes can be added using the admin.addTrustedPeer() call in the Javascript console and removed using admin.removeTrustedPeer() call.
admin.addTrustedPeer("enode://f4642fa65af50cfdea8fa7414a5def7bb7991478b768e296f5e4a54e8b995de102e0ceae2e826f293c481b5325f89be6d207b003382e18a8ecba66fbaf6416c0@33.4.2.1:30303")
Summary
Geth connects to Ethereum Mainnet by default. However, this behaviour can be changed using combinations of command line flags and files. This page has described the various options available for connecting a Geth node to Ethereum, public testnets and private networks.